The Baroque church of the Holy Trinity or commonly known as the Premonstratensian church was the site of the martyrdom of three saints in 1619. It the Middle Ages, the Royal House (a seat of the Royal Chamber), stood on the site of the present church. In 1618, at the beginning of the Counter-Reformation and the start of the Thirty Year War, The captain of the city established there a dwelling and a chapel for Jesuits in the Protestant town. Two Jesuits Melicher Grodecký, Štefan Pongrác were sent there, to work with a canon Marek Križin. On 7 September 1619, the forces of George I Rákóczi, the father of the Prince of Transylvania George II Rákóczi, stormed the castle and arrested the priests. They gave them a death sentence on charges of treason; accusing them of inviting the Polish army into Kassa. They were tortured and then beheaded that day. The execution of the priests shocked the local population, Catholics and Protestants alike.
In 1657, the Bishop of Eger, Benedict Kishdy, founded the first Košice University (Universitas Cassoviensis) close to the site. Later, the daughter-in-law of George I Rákóczi, Sofia Bathory, wife of George II Rákóczi, bought the ruins of the former Royal House with intention of building a church for the Jesuits there to make amends for the events of the Thirty Years' War. In 1681, construction on the church finished and it was opened.
On 21 July 1773, the Jesuits was expelled from the city as part of the suppression of the Society of Jesus. So in 1811, the church was given to Premonstratensians who currently administer the church.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.