The exact construction period of Rõngu vassal fortress is not known, but it was probably completed around 1340. The Holy Cross Chapel, located here, was mentioned in the year 1413. During the Middle Ages, the stronghold belonged to the Tödwen family. The fortress was destroyed by the troops of the Order in 1558 and burnt by Jesuits in 1625.
The majority of the castle's layout is not visible over the ground surface. An approximately 25-metre-long section from the outer wall of the eastern side has been preserved, there is also the opening of the main gate. The ruins have not been conserved and fall down gradually. The castle hill is surrounded by a 12-hectare park, which has beautiful majestic oaks, larches and other ancient trees.
Reference: Võrtsjärv Travel Guide
The Chapel of St. Martin is the only completely preserved Romanesque building in Vyšehrad and one of the oldest in Prague. In was built around 1100 in the eastern part of the fortified outer ward. Between 1100 and 1300, the Rotrunda was surrounded by a cemetery. The building survived the Hussite Wars and was used as the municipal prison of the Town of the Vyšehrad Hill.
During the Thirty Years’ War, it was used as gunpowder storage, from 1700 to 1750, it was renovated and reconsecrated. In 1784, the chapel was closed passed to the military management which kept using it as a warehouseand a cannon-amunition manufacturing facility. In 1841, it was meant to be demolished to give way to the construction of a new road through Vyšehrad. Eventually, only the original western entrance was walled up and replaced with a new one in the sountren side. The dilapidating Rotunda subsequently served as a shelter for the poor.