30.03.2026

The Cross in Art

Building design

The Gero cross in Cologne Cathedral is one of the oldest depictions of Christ on the cross. Photo: CC BY-SA 3.0, via: Wikimedia Commons

Hardly any symbol has shaped Western art history as profoundly as the cross. What began as a cruel instrument of Roman execution became the central symbol of Christianity—and one of the most versatile motifs in European art. A journey through two millennia of visual history.

There are symbols we’ve seen so often that we’ve stopped truly noticing them. The cross is one of them. It hangs on church walls and museum facades, adorns altar spaces and jewelry, and appears in modernist abstraction just as much as in medieval goldsmithing. And yet behind this seemingly simple form—two intersecting lines—lies one of humanity’s most complex visual histories.
For the cross was not originally a religious symbol, but an instrument of death. Roman crucifixion was one of the most brutal methods of execution in antiquity, deliberately staged in public and designed to be humiliating. That this symbol, of all things, became the emblem of a world religion is, from a historical perspective, one of the most astonishing reinterpretations ever—and art has accompanied, documented, and helped shape this process of transformation over the centuries.

From a Symbol of Shame to a Sacred Symbol: The Early Centuries

In the first centuries of Christianity, the cross scarcely appeared in the visual arts. The early Christians, who suffered persecution, used other symbols—the fish, the lamb, the anchor. The cross was too heavily associated with disgrace and torture to be used openly as a symbol.
That did not change until after the Edict of Milan in 313, which guaranteed Christians religious freedom in the Roman Empire. Emperor Constantine had the cross minted on coins and affixed to military standards. From then on, an artistic process of transfiguration began: The cross was gilded, set with precious stones, and immortalized in mosaics. This is particularly striking inthe so-called*Crux gemmata*, the gem-set cross, as seen, for example, in the 6th-century mosaics of Sant’Apollinare in Classe in Ravenna —a radiant, richly set cross that proclaims not suffering but triumph. Christ’s death was deliberately omitted from this early visual language; what mattered was the Resurrection.

Pain and Humanity: The Crucifix in the Middle Ages

This changed fundamentally during the High Middle Ages. The more theology focused on Christ’s sacrificial death, the more corporeal the art became. The living, triumphant Christ on the cross gave way to a different depiction: the suffering, dying, bleeding body.
TheGerokreuzin Cologne Cathedral, created around 970, is considered one of the earliest examples of this new visual language. It depicts Christ not as a victor, but as a dying man—his head bowed, his body heavy. This shift was not an artistic fad, but a theological statement: God truly suffered. This message was intended to strike a chord with the faithful, both emotionally and existentially.
The suffering crucifix reached its peak in the Late Gothic period. Matthias Grünewald’sIsenheim Altarpiece(completed around 1515) is perhaps the most radical work in this regard in the history of Western art. Grünewald’s Christ is covered in wounds, his body contorted, his hands clenched. The work was created for an Antonite monastery that cared for plague victims and those afflicted with skin diseases—the patients were meant to recognize their own suffering in Christ’s body. Rarely has art been so directly aimed at offering comfort through compassion.

Abstraction and Reinvention: The Cross in Modern Art

With the Enlightenment and secularization, the cross lost its inherent religious association—and thereby gained new artistic freedoms. In the 20th century, it became an object of formal exploration, political significance, and spiritual reinvention. Piet Mondrian, who came from a strictly Calvinist family, constructed his famous grid paintings from horizontal and vertical lines—a structure that inevitably evokes the cross without ever explicitly depicting it. Mark Rothko, who conceived his large-scale color-field paintings as spaces for spiritual experience, spoke openly of a religious atmosphere beyond denominational ties. And Barnett Newman created an abstract Passion with his series*The Stations of the Cross*(1958–1966)—black and white stripes on canvas that evoke the fourteen Stations of the Cross without a single figurative element.
At the same time, the cross became a means of provocation in contemporary art. Andres Serrano’s controversial photograph*Piss Christ*(1987) depicted a crucifix submerged in glowing yellowish urine—an image that sparked massive protests and is still debated today. Regardless of one’s own stance on the matter, it makes one thing clear: even after two millennia, the cross is not a neutral symbol. It moves us, wounds us, comforts us—and it provokes us.
What keeps the cross so enduringly alive as an artistic motif is its complexity. It embodies death and resurrection, pain and hope, history and the present all at once. No other symbol in the Western visual tradition has been reimagined, reinterpreted, and reexamined so often. Artists still turn to it—not because it is convenient or familiar, but because it continues to convey something that cannot be translated into any other form. Two lines. Countless meanings.

12.06.2026

Uncategorized

Certificate of Compliance: Fire Protection—Fundamentals, Calculations, and Practice

Building design

A structural detail of the building related to the fire safety compliance certification — Four fire extinguishers on a green wall—a quiet snapshot of everyday architecture. Photo: jandira_sonnendeck

Anyone who puts a building into service assumes responsibility for more than just aesthetics and functionality. The fire safety compliance certificate is the legal and technical instrument used to demonstrate that the installed construction products and building systems actually meet the requirements that were a prerequisite for the planning and approval processes. It lies at the intersection of product law, building code regulations, and structural testing practices, and is equally binding and significant for architects, specialist planners, and building owners.

What the Fire Safety Certificate of Conformity Means Legally and Technically
Which legal bases and standards define and regulate this instrument
How the conformity confirmation process works in practice
Which construction products and building systems are affected and why
What role conformity marks, test certificates, and certificates of suitability play
Who issues the confirmation, who reviews it, and who bears responsibility
What typical errors occur in practice and how they can be avoided
How the confirmation of conformity fits into the overall system of structural fire protection

Definition and Legal Basis: What the Fire Protection Declaration of Conformity Is

The fire protection conformity certificate is a written declaration confirming that a construction product or building system complies with the requirements relevant to its use in fire protection. These requirements may stem from a general building authority approval (abZ), a general building authority test certificate (abP), a European Technical Assessment (ETA), or a case-by-case approval (ZiE). The declaration is not a marketing document or voluntary certification, but rather an instrument required by building codes that documents the transition from abstract product characteristics to concrete use in construction.

The legal basis lies in the state building codes of the German federal states, which are largely based on the Model Building Code (MBO). The MBO distinguishes between regulated and unregulated construction products. Regulated construction products comply with a technical building regulation or a harmonized European standard and may be used without further proof, provided they bear the conformity mark (Ü mark). Non-regulated construction products require separate proof of suitability for use, which is provided by the aforementioned instruments. For construction products relevant to fire protection, a higher level of requirements applies because failure in the event of a fire can pose an immediate threat to life.

The Ü mark, which is affixed to regulated construction products, is the visible symbol of the declaration of conformity. It indicates that the manufacturer declares that its product complies with the applicable technical regulations. For construction products that are not covered by harmonized European standards but perform fire protection functions, the fire protection declaration of conformity is the key proof that bridges the gap between product approval and installation. Without it, there is no formal proof that the product used is in fact what the approval specified.

The System of Proofs of Suitability: Approvals, Test Certificates, and Standards

To properly understand the fire safety declaration of conformity, one must understand the system of proof of suitability in which it is embedded. This system has several levels that apply differently depending on the product type and application. At the foundation are harmonized European standards (hEN), which are adopted under the Construction Products Regulation (EU Regulation No. 305/2011, or CPR for short). Products that comply with such a standard bear the CE marking; however, this marking does not constitute approval for use under national law but merely declares the product’s performance characteristics.

For products without a harmonized standard or for applications that fall outside the scope of a standard, national instruments apply. The General Building Authority Approval (abZ) is issued by the German Institute for Building Technology (DIBt) in Berlin and fully describes the permissible conditions of use for a product. The General Building Inspection Test Certificate (abP) is a simplified instrument for products whose suitability for use can be demonstrated through testing without the need for a full approval. Both documents contain precise information on installation conditions, processing instructions, and maintenance requirements that are directly relevant to the subsequent confirmation of compliance with fire safety standards.

Since the amendment of the Construction Products Act, the DIBt has gradually supplemented or replaced the general building authority approval with the general type approval (aBG) and the general building authority test certificate with the general type test certificate (aBPZ). These terms no longer refer solely to the product itself, but to the construction type—that is, the combination of product, installation situation, and installation rules. This distinction is significant for fire protection: A fire protection system, such as a cable penetration or a fire damper, will only function as tested if all components and the installation precisely comply with the specifications of the proof of suitability for use. The fire protection conformity confirmation is the document that confirms exactly this for the specific construction project.

Who issues the Fire Safety Conformity Certificate, and who bears responsibility?

The issue of responsibility is particularly sensitive in fire protection because defects can have irreversible consequences in an emergency. Depending on the product and the level of requirements, the Fire Safety Conformity Certificate can be issued in two ways: by the manufacturer itself or by a recognized testing, inspection, and certification body (PÜZ body). The applicable method is determined by the respective proof of suitability for use. For simpler products with a lower risk potential, the manufacturer’s declaration is sufficient; for safety-critical construction products with high fire safety requirements, third-party monitoring by an accredited body is mandatory.

By issuing a declaration of conformity, the manufacturer makes a legally binding statement that its product meets the requirements of the declaration of suitability for use. This declaration requires an in-house production control system (WPK)—that is, an internal quality management system that ensures consistent manufacturing quality. The WPK is not an informal tool, but a normatively required component of the proof of conformity. For products subject to third-party supervision, the in-house production control is supplemented by regular audits conducted by the PÜZ body, which makes the right to award the conformity mark contingent upon ongoing compliance with the requirements.

On the construction site, the contractor is responsible for ensuring that only products with a valid certificate of conformity are installed and that the installation complies with the specifications of the certificate of suitability. The architect or specialist planner is required to request, review, and document the certificates of conformity. The building inspection authority may require the submission of these documents as part of its construction supervision. In practice, the documentation chain is often incomplete because the importance of the fire protection certificate of conformity is underestimated on the construction site, and the pressure of the construction schedule takes precedence over the careful filing of supporting documents.

The Role of the Fire Protection Planner and the Expert

In buildings classified as Class 4 and 5, as well as in special-purpose structures, many federal states require the involvement of a qualified fire protection planner or a recognized fire protection expert. This expert not only reviews the fire protection concept during the planning phase but also oversees the construction process and ultimately confirms that the completed building complies with the approved fire protection concept. The certificates of conformity for the installed fire protection products are an essential part of the expert’s basis for review. Without complete supporting documentation, the expert cannot issue the final certificate, which prevents the building from being put into use.

Typical Fire Protection Products and Their Compliance Requirements

The range of construction products for which a fire protection conformity certificate is required extends from building materials and components to complex systems. Among the most common product groups are fire dampers in ventilation and air-handling systems, cable penetrations and pipe penetrations in ceilings and walls, fire-rated doors and gates, fire-resistant glazing, fire-resistant coatings (so-called reactive fire protection systems that foam up and insulate in the event of a fire), fire-resistant plasters and panels, as well as insulation materials with a fire protection classification.

Each of these product groups has specific requirements regarding proof of suitability for use and the type of conformity assessment. A fire damper, for example, must not only be the correct product; it must also be installed in the correct wall construction, with the correct fasteners, and with the correct control system in order to achieve the tested fire resistance rating. Deviations from the installation instructions in the proof of suitability—even if they seem plausible from a structural engineering perspective—void the validity of the confirmation of conformity. This principle of systemic conformity is not sufficiently understood by many tradespeople on the construction site and leads to one of the most common errors in structural fire protection.

Reactive fire protection systems—specifically coatings applied to steel structures that form an insulating layer by foaming in the event of a fire, thereby delaying the critical heating of the steel—deserve special attention. The effectiveness of these systems depends heavily on the coating thickness, the substrate, the application method, and the environmental conditions. The fire protection compliance certificate for such systems requires complete documentation of the coating thickness through measurement reports, which must be prepared by the applicator and archived by the client. If these records are missing, the certificate of compliance is not formally valid, even if the product was applied correctly.

Common Mistakes in Practice and How to Avoid Them

Practical experience reveals a recurring pattern of errors that can be divided into three categories: documentation gaps, product mix-ups, and installation errors. Documentation gaps arise when certificates of compliance are available but are not systematically collected, organized, and handed over to the building owner. Complete fire protection documentation is essential for subsequent use, maintenance, and any potential renovations. If it is missing, a time-consuming assessment by experts must be conducted in cases of doubt—a process that is expensive and rarely provides complete certainty.

Product mix-ups occur when a similar but not identical product is installed on the construction site because the one originally planned is temporarily unavailable. Any product change in the area of fire protection requires a new review to determine whether the new certificate of suitability applies to the specific installation situation and whether a fire protection conformity certificate is available for the replacement product. This verification step is often skipped in day-to-day construction site operations because it takes time and the urgency of the problem is not immediately apparent.

Installation errors are the most serious category. They occur when the installation instructions in the certificate of suitability are not followed—whether due to ignorance, a tendency to cut corners, or because the instructions in the document are difficult to understand. Typical installation errors with cable penetrations include the use of incorrect filling materials, insufficient fastening, or the mixing of products from different manufacturers that have not been tested together. For fire-rated doors, common errors include incorrectly adjusted door closers, missing or improperly installed seals, and subsequent modifications to the frame or door leaf that invalidate the certification.

To avoid these errors, a structured fire protection management system on the construction site is recommended, comprising the following elements:

Early specification of all fire protection-related products in the request for proposals, with an explicit requirement for a certificate of conformity
Establishment of a central document folder for all fire safety certifications on the construction site
Training of the contractors on the specific installation instructions for the products used
Random inspections of installation sites by the site manager or fire safety planner during construction
Full handover of the documentation to the building owner as part of the building documentation

The Fire Safety Declaration of Conformity in the European Context

The German system of conformity certification does not exist in isolation but is in tension with the European Construction Products Regulation. The Construction Products Regulation governs the CE marking of construction products and creates a single European market for these products. However, it expressly does not regulate the use of these products under national building codes. This means that a product with CE marking and a declared fire protection performance may not automatically be installed in Germany if a national approval or proof of suitability for use is required for the specific application.

In practice, this duality leads to confusion. Manufacturers from other EU countries who supply their products with CE marking and a declaration of performance are often surprised that additional documentation is required for the German market. Conversely, German planners and building owners must carefully verify, in the case of imported products, whether the CE marking is sufficient for the intended use or whether a national certificate of suitability—and thus a confirmation of compliance with fire protection requirements under German law—is required. The DIBt and the state building authorities have published guidance on this matter; however, this guidance must be updated regularly because the European standards framework is constantly evolving.

European Technical Assessments (ETAs) issued by the DIBt or another authorized Technical Assessment Body may, in certain cases, be recognized as proof of suitability for use under German law. For fire protection products, however, this is subject to strict conditions, because while the European classification standards (in particular the EN 13501 series) harmonize test methods and classifications, the national requirements for fire resistance classes and installation conditions remain enshrined in national law. The fire protection certificate of conformity thus remains a genuinely national instrument, even if the products to which it refers may have been tested and classified at the European level.

Context: Why the Fire Safety Declaration of Conformity Is More Than Just Bureaucracy

It would be a mistake to view the fire safety declaration of conformity as a mere administrative requirement to be fulfilled with as little effort as possible. It serves as the link between the abstract verification of product properties and concrete safety within the building. A fire protection system that has achieved the required fire resistance class in the laboratory will only provide protection in an emergency if it has also been correctly installed and documented on site. The certificate of conformity is the formal proof that this transition has been successfully completed.

For architects and specialist planners, this entails a dual responsibility: they must not only specify the correct products but also ensure that the installation and documentation meet the requirements. This responsibility does not end with the handover of the building, because subsequent changes to fire protection-relevant building components—such as replacing a fire door or retrofitting conduits with certified fire barriers—require new, valid certificates of conformity. Failure to do so not only jeopardizes the building’s operating permit but also results in significant liability in the event of damage.

This issue is gaining importance due to the increasing complexity of modern buildings and the growing density of technical installations. Buildings with extensive building services, data centers, laboratories, or special usage requirements have a multitude of penetrations, fire-resistant barriers, and fire protection systems, each of which requires its own documentation. In this context, the fire protection compliance certificate is not a single document but a structured verification system that must accompany the building throughout its entire service life. Those who consistently implement this system from the very beginning not only ensure legal compliance but also lay the foundation for a permanently effective level of fire protection that truly lives up to its name.

11.12.2024

The light of history

Building design

The extensions stand out clearly from the brick and glass architecture of the historic waterworks.

The small town of Mons in Belgium has a turbulent past. In the Mons Memorial Museum by architect Pierre Hebbelinck, the light and dark sides of its history find architectural expression.

Buffer zone, border area, battlefield: Belgium has historically always been a crossroads of European history – and therefore also a stage for its often tragic chapters. This is particularly evident during a visit to the Mons Memorial Museum, which opened in 2015 and is located in the small town of Mons in the southern part of the country.

Pierre Hebbelinck from Liège was commissioned in 2011 to convert a historic industrial building into a museum dedicated to the history of the region. The brick, iron and glass waterworks is a typical witness to the economic boom that the Walloon region experienced during the industrialization process in the 19th century and had to be renovated and extended in line with the preservation order.

The architects opted for two wing extensions, whose exterior façades were painted white to clearly distinguish the new buildings from the existing ones. They clearly divided the functions between the three buildings, with the interior design of the individual rooms corresponding to the exhibition content: the windowless, oppressive rooms of the new buildings focus on the most dramatic chapters of local history – war, deportation, occupation – while the large hall of the old building is dedicated to liberation, democracy and freedom.

The view outside

The hall in the middle of the complex, glazed at the gable ends, serves as a transparent reception and catering area and is crossed by a 15-metre-long walkway. This connects the permanent exhibition in the left wing with the rooms for temporary exhibitions in the right wing.
The architects attached great importance to the lighting concept: in addition to the lighting, which is differentiated according to function, the historic glass fronts of the listed old building were also professionally refurbished to optimize the incidence of sunlight and improve the quality of stay for visitors to the café and bookshop. The large glass windows, which are divided by metal bars, were also renewed.

Open and closed

The closed nature of the extensions forms a contrast to the open and transparent existing building. A strategically placed aisle in the exhibition tour leads to an open space in the basement, whose brick-clad, monotonous red walls can be read as an architectural image of the tragic wartime past of the Mons region. There are also narrow windows that allow light into the interior like crevices in a rock, or provide a view to the outside at certain points: For example, to a war memorial at the crossroads or to important elements of the city’s history in the public space.

Photos: François Brix.