The city grows: an evaluation at the end of the Middle Ages (1500 AD): The city grew throughout the Middle Ages and became the largest town in France. Under the Roman Empire the administrative capital was Lyon. During this period, this growth of Paris solved some problems but also raised others: From the beginning the city had evolved on three sites: the Ile de la Cité, the right bank and the left bank. From this initial reality it was necessary to try and create a single town. This was only partly realised. In 1420 there were five bridges in Paris. The enclosure of Philippe-Auguste brought together the three sites. But another problem arose: how to pass from a closed city to an open one. This problem remained for Paris until the 19th century, because two other enclosures were realised during the following centuries.