Historical summary
| 742 | First written mention of Erfurt |
| 1060 | The collegiate church is converted into a Benedictine abbey under Archbishop Siegfried I. |
| 1080 | Erfurt is conquered by Heinrich IV and the abbey is destroyed by fire |
1103 – 1147 | The new abbey and church of St Peter and St Paul is constructed in the Hirsau style |
| 1168 | The town’s fortifications are extended to include Petersberg hill |
| 1181 | Henry the Lion submits to Emperor Frederick Barbarossa at the Imperial Diet in St Peter’s Church |
| 1665 | The Archbishop of Mainz orders the construction of the citadel after he subjugates the city of Erfurt. The first construction phase in the new Italian style is shaped by Antonio Petrini, architect to the court of the Elector of Mainz. |
1707 – 1726 | Further construction under the stewardship of Maximilian von Welsch, a military architect from Mainz (second period of construction) |
| 1802 | The citadel receives a Prussian garrison |
| 1803 | St Peter’s Abbey is secularised and the church inventory is sold off |
1806 – 1813 | The citadel falls to the French army. During a visit, Napoleon orders that the fortifications be strengthened. The French garrison comes under fire, and St Peter’s Abbey and several of the citadel’s other buildings are destroyed |
| 1814 | The citadel once again falls into Prussian hands |
1815 – 1866 | Extension of the citadel based on a new Prussian fortification system (third period of construction) |
| 1820 | The remnants of the Romanesque basilica are covered with a tall roof and used to store flour and weapons |
| 1873 | Kaiser Wilhelm I orders the citadel’s fortifications to be removed, but only some are |
| until 1963 | Military use |
| from 1965 | Petersberg Citadel is repurposed |
| since 1990 | This important example of fortification architecture is restored, refurbished and opened up to visitors and local residents |