At the heart of the historical center of Strasbourg, the Cathedrale of Notre Dame is one of the finest of the great Gothic cathedrals. Standing on the site of a roman temple, the first version of the cathedral was begun in 1015 but fire destroyed most of the original Romanesque building. By the time rebuilding had begun at the end of the 12th century the Gothic style had reached Alsace, and stonemasons and master builders who had worked at Chartres brought their skills to Strasbourg. The cathedral's three portals are ornamented with statues, the south portal leading to the Gothic Pilier des Anges (Pillar of Angels). Adjacent to the pillar is the astronomical clock, a mid-19th-century version of the original 14th-century clock. The key time to see it in action is 12:30 p.m., when angels turn over hour glasses and the twelve apostles parade before Christ.