The 12th-century late Romanesque church of San Juan Bautista is attached to a 10th-century Berber tower, which is 18 metres tall with a 9.4x7.4 metre floor plan and 1.75-metre thick walls on all of its three floors. Originally it was built with the rammed earth technique but then the structure was changed to stonework. The access door to the tower is hidden in a passageway that connects the tower to the church. Later on, the windows were opened up to place bells inside, and the tower was covered with a roof.
References: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.