Can you go down there?
Not as a casual add-on to a tourist ticket. The underground rooms are a research site. Excavation tours are booked separately through the works yard. Some finds — especially the rich Frankish graves — are shown in the Treasury.
A former temporary west door from the unfinished gothic church was rebuilt underground and now serves as the archaeologists’ entrance. You will not walk through it on a standard visit.
Roman Cologne under the nave
The gothic church sits inside the old walled city. The north nave wall still follows the Roman town wall. Under the floor, excavators found street lines with drains and colonnades, plus heated rooms, wall painting and mosaics — a wealthy north-east neighbourhood, not a graveyard.
A bishop of Cologne is named as early as 313. That does not prove a church already stood on this exact corner. The first building that is clearly Christian comes later.
Frankish baptistery and graves
From the 6th century the site is a church. East of today’s choir, an octagonal baptismal basin was found in 1866 and left in place. The church that went with it sits under the gothic choir. Inside the walls — where Roman law had banned burials — excavators found Frankish graves, including a richly furnished young woman, often identified as Queen Wisigarde, and a small boy. Those grave goods are why the Treasury visit is worth the extra ticket even if you never see the hole they came from.
The altar of that first church sat almost exactly under today’s high altar, about four metres down.
The Old Cathedral
Around 800, Archbishop Hildebold — adviser to Charlemagne — replaced the earlier church with a building almost 100 metres long, two apses, atriums, side towers. Foundations of the west apse still lie under the gothic nave and fill nearly the whole width of the middle aisle. The plan matches the church drawn in the 11th-century Hillinus Codex.
In 1164 the relics of the Three Kings arrived from Milan. Wear on the Old Cathedral floor, including a fence line around a central rose, shows how tightly pilgrims were kept off the shrine. That crush is the practical reason the gothic rebuild began in 1248 on the same plot: there was no empty lot left in the medieval city.
Gothic foundations, 632 years of patches
The east end of the Old Cathedral came down first so the gothic choir could go up while services continued in the west. After the choir was consecrated in 1322, the rest of the old church was cleared. Early gothic footings are huge — blocks up to 16 metres deep in Cologne’s sand and gravel. Later bays are slimmer, as the lodge learned the ground.
When work stopped in the 16th century, only the lower south tower and a makeshift west door existed. That door was taken down in 1880 and rebuilt below. The finished west front you photograph from the station is the medieval design, completed with 19th-century iron and steam.
If you want the book, not the hole
Ulrich Back’s Archäologie im Kölner Dom (Verlag Kölner Dom) is the compact summary the works yard points to. Contact for the excavation office: Dombauhütte Köln, Roncalliplatz 2, 50667 Köln. This page does not sell tickets or run tours.
Cathedral history · Treasury · Shrine of the Three Kings · Legends
External: koelner-dom.de · Dombauhütte