Cologne's medieval builders had planned a grand structure to house the reliquary of the Three Kings and fit for its role as a place of worship for the Holy Roman Emperor.

[10] However, Cologne's Christian community, still small at this time, did not gather in a church, but in a residential building, which is thought to have been located on the cathedral hill below today's choir.

[11] After the collapse of Roman rule on the Rhine, the Merovingian petty kings residing in Cologne built an episcopal church on this site in the 6th century, which was eventually around 40 to 50 meters long and equipped with an ambon.

Already in late antiquity, there was a baptistery to the east of the cathedral choir, where the early Christians, following the rite of the time, stepped into knee-deep water and were completely doused.

It is assumed that the baptismal font (piscina), which dates back to the 5th century, was originally located in the garden of the Roman house that served as a Christian meeting place.

[13] Later, the baptistry built above the pool was presumably combined with the cathedral church to form a single building complex, although there is no archaeological evidence of this today.

This work ceased in 1473, leaving the south tower complete to the belfry level and crowned with a huge crane that remained in place as a landmark of the Cologne skyline for 400 years.

[32][page needed] Some work proceeded intermittently on the structure of the nave between the west front and the eastern arm, but during the 16th century this also stopped.

[33][page needed] With the 19th-century Romantic enthusiasm for the Middle Ages, and spurred by the discovery of the original plan for the façade, the Protestant Prussian Court working with the church, committed to complete the cathedral.

It was achieved by civic effort; the Central-Dombauverein, founded in 1842, raised two-thirds of the enormous costs, while the Prussian state supplied the remaining third.

[citation needed] The state saw this as a way to improve its relations with the large number of Catholic subjects it had gained in 1815, but especially after 1871, it was regarded as a project to symbolize German nationhood.

[34] Work resumed in 1842 to the original design of the surviving medieval plans and drawings, but using more modern construction techniques, including iron roof girders.

[citation needed] The completion of Germany's largest cathedral was celebrated as a national event on 15 October 1880, 632 years after construction had begun.

[36] The twin spires of the cathedral were an easily recognizable navigational landmark for Allied aircraft bombing during World War II.

On 6 March 1945, an area west of the cathedral (Marzellenstrasse/Trankgasse) was the site of intense combat between American tanks of the 3rd Armored Division and a Panther Ausf.

A nearby Panther, a German medium tank, was sitting by a pile of rubble near a train station right by the twin spires of the Cologne Cathedral.

A repair to part of the northwest tower, carried out in 1944 using poor-quality brick taken from a nearby ruined building, remained visible as a reminder of the war until 2005, when it was restored to its original appearance.

[39] Repair and maintenance work is constantly being carried out in the building, which is rarely free of scaffolding, as wind, rain, and pollution slowly eat away at the stones.

[41] The then archbishop of the cathedral, Cardinal Joachim Meisner, who had preferred a figurative depiction of 20th-century Catholic martyrs for the window, did not attend the unveiling.

[52] The filigree buttresses and arches are exposed to the weather from all sides[53] and are attacked by water, the sulphur content of the air and bird droppings.

It is therefore constantly being renewed and until the 1980s was preferably replaced with Londorf basalt lava, which is considered to be very weather-resistant, but is not sandy beige, but grey in color.

[60] From May to November 2021, a remote-controlled drone took 200,000 high-resolution photos of all parts of the façade from a distance of five to seven meters and assembled them into a digital 3D model of the cathedral, which offers a very accurate representation with 25 billion polygons.

It has two aisles on either side, which help support one of the very highest Gothic vaults in the world, being nearly as tall as that of the Beauvais Cathedral, much of which was never built or had collapsed.

The choir retains a great many of its original fittings, including the carved stalls, despite French Revolutionary troops having desecrated the building.

A set of five on the south side, called the Bayernfenster, were a gift from Ludwig I of Bavaria, and strongly represent the painterly German style of the time.

Externally, particularly from a distance, the building is dominated by its huge spires, which are entirely Germanic in character, being openwork like those of Ulm, Vienna, Strasbourg and Regensburg Cathedrals.

[64] The most celebrated work of art in the cathedral is the Shrine of the Three Kings, commissioned by Philip von Heinsberg, archbishop of Cologne from 1167 to 1191 and created by Nicholas of Verdun, begun in 1190.

The shrine takes the form of a large reliquary in the shape of a basilican church, made of bronze and silver, gilded and ornamented with architectonic details, figurative sculpture, enamels and gemstones.

Embedded in the interior wall are a pair of stone tablets on which are carved the provisions formulated by Archbishop Englebert II (1262–67) under which Jews were permitted to reside in Cologne.

On Thursday, 3 March 2022, landmark cathedrals across Europe chimed in unison "in a gesture of solidarity with Ukraine, as bystanders gathered to mourn those killed during Russia's invasion and pray for peace."