ravelins called Anselm and Lotha, the main gateway (Peterstor) and commandant building, three barracks, which are among the oldest surviving barracks in Germany, and the tunnels within the walls, called Horchgänge in German, meaning the 'listening passages'. The second construction phase was from 1707 to 1728, under the direction of the architect Maximilian von Welsch (1671–1745), who was made an imperial knight with the title Edler von Welsch for his services to architecture by Charles VI, Holy Roman Emperor in 1714. Welsch put special emphasis on the reinforcement of the fortress and trench defenses. Erfurt became part of the Kingdom of Prussia in 1802, to compensate Prussia for its territories on the left bank of the Rhine that were lost to France. However, on 16 October 1806 Erfurt was handed over to French forces in what is known as the Capitulation of Erfurt, which followed the Prussian defeat in the Battle of Jena–Auerstedt. Napoleonic period (1806–1814) French troops were stationed at Erfurt from 1806 to 1814, when Erfurt was under Napoleonic occupation. Napoleon arrived in the city on 23 June 1807, and created the Principality of Erfurt, which he ruled directly himself. Napoleon visited Erfurt a number of times during the French occupation. He took a particular interest in Petersberg Citadel. He stayed in Erfurt from 27 September to 14 October 1808, when he meet with Tsar Alexander I of Russia for the Congress of Erfurt. The two leaders visited Petersberg Citadel together during the Congress. He also went to Erfurt on 15 December 1812 on his return from Russia to France, and from 25–28 April 1813. On 21 April 1813 he had ordered that Petersberg Citadel should be strengthened and equipped so that it could support 2000 men under siege for six months. Both French troops and civilian residents of Erfurt were put to work on the project, with over 3000 civilians working on building the ditches that surround the external walls. The work was carried both day and night, used flaming torches to see by. During this time a hidden trench connecting Petersburg and Cyriaksburg citadels was built, the remains of which can still be seen at Cyriaksburg today. On 4 November 1813 Prussian, Austrian and Russian forces drew in on Erfurt and sought to get the French to surrender and leave Petersberg Citadel. There was no surrender and fire was opened on the citadel on 6 November,