It was built on the site of a 4th century Roman temple, a square edifice known as the 'oldest cathedral' and commissioned by Maternus, the first Christian bishop of Cologne.
The present cathedral was built to house the relics of the Magi, brought to Cologne from Italy by Archbishop Rainald von Dassel in 1164. The foundation stone was laid on August 15, 1248, by Archbishop Konrad von Hochstaden. The choir was consecrated in 1322. After this initial rapid progress, construction work gradually came to a standstill, and by the year 1560, only a torso had been built. It was only with 19th century romantic enthusiasm for the Middle Ages and the commitment of the Prussian Court that construction work resumed in 1842 with the addition of the towers and other substantial parts of the cathedral. The completion of Germany's largest cathedral was celebrated as a national event in 1880, 632 years after construction had began. The celebration was attended by Emperor Wilhelm I.
In the end, the outer appearance remained faithful to the original medieval plans; however, the roof was a modern steel construction. At its completion, the Cologne cathedral was the tallest building in the world, having taken over from the cathedral of Rouen. In 1889, it lost the title to Mole Antonelliana, the cathedral of Turin.
The most celebrated work of art in the cathedral is the Sarcophagus of the Magi, a large gilded sarcophagus dating from the 13th century, and the largest reliquary in the western world. It is thought to hold the remains of the Three Wise Men. See: Shrine of the Three Kings at Cologne Cathedral.
The Gero Cross (Gero-Kreuz) (around 970 AD), near the sacristy, is the oldest large cross north of the Alps. In the Sacrament Chapel, the "Milan Madonna" (Mailänder Madonna), dating from around 1290, is a wooden sculpture depicting Mary and the child Jesus. In St. Mary's Chapel (Marienkapelle) is the altar of the patron saints of Cologne with an altar piece by Stephan Lochner. Other outstanding works of art are to be found in the cathedral treasure chamber.