In 1164, the Archbishop of Cologne, Rainald of Dassel acquired the relics of the Three Kings which the Holy Roman Emperor, Frederick Barbarossa had taken from the Basilica of Sant'Eustorgio, Milan, Italy. (Parts of the relics have since been returned to Milan.) The relics have great religious significance and drew pilgrims from all over Christendom. It was important to church officials that they be properly housed, and thus began a building program in the new style of Gothic architecture, based in particular on the French cathedral of Amiens.
The foundation stone was laid on 15 August 1248, by Archbishop Konrad von Hochstaden. The eastern arm was completed under the direction of Master Gerhard, was consecrated in 1322 and sealed off by a temporary wall so it could be in use as the work proceeded. Eighty four misericords in the choir date from this building phase. In the mid 14th century work on the west front commenced under Master Michael. This work halted in 1473, leaving the south tower complete up to the belfry level and crowned with a huge crane that remained in place as a landmark of the Cologne skyline for 400 years.
With the 19th century romantic enthusiasm for the Middle Ages, and spurred on by the lucky discovery of the original plan for the facade, it was decided, with the commitment of the Protestant Prussian Court, to complete the cathedral. It was achieved by civic effort; the Central-Dombauverein, founded in 1842, raised two-thirds of the enormous costs (over US$ 1 billion in today's money), while the Prussian state supplied the remaining third. The state saw this as a way to improve its relations with the large number of Catholic subjects it had gained in 1815.
Work resumed in 1842 to the original design of the surviving medieval plans and drawings, but utilizing more modern construction techniques, including iron roof girders. The nave was completed and the towers were added. The bells were installed in the 1870s.
The completion of Germany's largest cathedral was celebrated as a national event on 14 August 1880, 632 years after construction had begun.