The towering Cathedral of St. Peter and St. Mary, Kölner Dom, on the banks of the Rhine is Cologne's most impressive landmark. This masterpiece of High Gothic architecture, one of the largest cathedrals in Europe, was begun in 1248 and was the most ambitious building project of the Middle Ages. As imposing as its façade, its magnificent interior covers an area of 6,166 square meters and boasts 56 huge pillars. Above the high altar is the Reliquary of the Three Kings, a 12th-century work of art in gold designed by Nicholas of Verdun to house the relics of the Three Kings