The oldest part of the Sjonhem church is the tower, which was built in the 13th century. Originally it was attached to a much smaller Romanesque church. The choir and nave was however torn down and replaced with the current structure during the middle of the 13th century.
Inside, church frescos decorate the vaults; these also date from the 13th century. Also probably original are some stained glass windows. A crucifix on the altar is somewhat later, dating from the 14th century. The baptismal font is however considerably older, dating from the 12th century and thus older than the church itself. It was made by the stonemason known as Hegvald. The church has been largely unaltered since the Middle Ages; the greatest change occurred in 1818 when the sacristy was built.References:
The Petersberg Citadel is one of the largest extant early-modern citadels in Europe and covers the whole north-western part of the Erfurt city centre. It was built after 1665 on Petersberg hill and was in military use until 1963. It dates from a time when Erfurt was ruled by the Electors of Mainz and is a unique example of the European style of fortress construction. Beneath the citadel is an underground maze of passageways that can be visited on guided tours organised by Erfurt Tourist Office.
The citadel was originally built on the site of a medieval Benedictine Monastery and the earliest parts of the complex date from the 12th century. Erfurt has also been ruled by Sweden, Prussia, Napoleon, the German Empire, the Nazis, and post-World War II Soviet occupying forces, and it was part of the German Democratic Republic (East Germany). All of these regimes used Petersberg Citadel and had an influence on its development. The baroque fortress was in military use until 1963. Since German reunification in 1990, the citadel has undergone significant restoration and it is now open to the public as a historic site.