Ilmmünster Abbey was formerly a collegiate foundation and originally a Benedictine monastery. The original site was a Benedictine monastery, founded in about 762 by the brothers Adalbert and Otker, traditionally supposed to be members of the Huosi, an ancient Bavarian noble family. The monastery was dedicated to Saints Arsatius, whose relics were here, and Quirinus, whose relics were at Tegernsee Abbey, founded by the same brothers, to which Ilmmünster was affiliated.
A collegiate foundation was also set up here in 1060. In 1493, the monastery was transferred to the Frauenstift in Munich, leaving the site for the Kollegiatstift. The property and assets were sold off in 1802 during secularisation, but the impressive church remains.
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.