The decline of the Roman Empire brought with it a decrease in the city's population and it took Strasbourg several centuries before its political and geographical importance restored its prestige.
At the end of the 10th century, the Bishop was granted authority over the city by the Emperor, and this led to the resurgence of trade in Strasbourg and also to its urban development. The city was rebuilt within the restored Roman perimeter wall, while the foundations of the future Cathedral were laid, cutting across the old via principalis (rue du Dôme). Urbanisation spread beyond the boundaries of the old Roman camp, to cover some 30 or so hectares to the south-west of the original island.
In 1262, Strasbourg became a free city of the Germanic Holy Roman Empire, under the authority of a Magistrate. Behind its impressive fortified walls, power within this mini republic was based in the Pfalz, or town hall, built in 1322 in the new geographical centre of the city, right next to what is now place Gutenberg. Two other buildings were constructed next to the Pfalz, the Chancellery in 1462, and the Palais de la Monnaie (the Mint), in 1507. The new buildings oversaw the transfer of power from the religious authorities in the place de la Cathédrale and place du Château.
Trade was vital to the city's economy, and tradesmen set up in districts protected by the outer wall (the quai des Bateliers, rue d’Or and rue des Bouchers). The whole of the island part of the city was now surrounded by a wall with a wall-walk for patrols and a series of watchtowers, including a number of square-shaped towers such as those which can still be seen today at the Ponts Couverts.
A double-wall system was built in the north of the city on either side of the river Ill, enclosing a strip of land upon which was built a wall and its gate towers (the false rampart, which ran parallel to the main wall).
At the end of the 14th century, the local authorities decided to protect the outlying West and North West parts of the city by a new wall, with three gates into the city (faubourg National and faubourg de Pierre and porte de Saverne).
The final extension in the Middle Ages was built mainly to protect the strategic position of the city and defend access to the Rhine. The Krutenau district, in the south-east of the city, was the nearest and a wall was built around it.
It was also around this time that a number of monasteries, churches and cemeteries within the city walls were demolished, freeing land up for Strasbourg's first "embellishments", which were carried out in place Gutenberg, the emblematic centre of the city's life at the time. In the same square, in 1579, the Magistrate ordered the construction of the Neubau ("new building" - now the Chamber of Commerce) to house the expanding municipal services and provide additional land for trade.
From 1576, the city underwent major changes as it sought to protect its outskirts and erect a defensive system to resist sieges. The defences were further strengthened right up to the 17th century, notably with the addition of fortifications designed by French military architect, Vauban.
As its outer wall expanded, the city reached a surface area of 202 hectares by the end of the 15th century. No further expansion would take place until 1871.