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:
First record of Kastelholma (or Kastelholm) castle is from the year 1388 in the contract of Queen Margaret I of Denmark, where a large portion of the inheritance of Bo Jonsson Grip was given to the queen. The heyday of the castle was in the 15th and 16th centuries when it was administrated by Danish and Swedish kings and stewards of the realms. Kastelhoma was expanded and enhanced several times.
In the end of 16th century castle was owned by the previous queen Catherine Jagellon (Stenbock), an enemy of the King of Sweden Eric XIV. King Eric conquered Kastelholma in 1599 and all defending officers were taken to Turku and executed. The castle was damaged under the siege and it took 30 years to renovate it.
In 1634 Åland was joined with the County of Åbo and Björneborg and Kastelholma lost its administrative status.