The site of the Notre dame is the cradle of Paris and has always been the religious center of the city. The Celts had their sacred ground here, the Romans built a temple to worship Jupiter. A Christian basilica was built in the sixth century and the last religious structure before the Notre-Dame construction started was a Romanesque church.It took until 1345 before the cathedral was completed, partly because the design was enlarged during construction. The result is an overwhelming building, 128 meters long (420 ft) with two 69 meter tall towers (226 ft). The spire over the crossing reaches 90 meters (295 ft) and was added in the nineteenth century by Viollet-le-Duc. The Notre-Dame Cathedral has several large rose windows, the northern thirteenth-century window is the most impressive. The massive window has a diameter of 13.1 meter.It wasn’t until the nineteenth century before the Cathedral was fully restored thanks in part to the writer Victor Hugo, who with his book ‘Notre-Dame de Paris’, made the Parisians realise the cathedral was worth restoring. The twenty-year-long restoration was led by a local architect, Eugène Emmanuel Viollet-le-Duc. Viollet-le-Duc made drastic, controversial modifications to the building and even added a spire. The cathedral was restored again between 1991 and 2001, this time the historic architecture was carefully preserved.