From 1156 to 1159, the Knights Hospitaller received land south of the bishop’s court, near the bridgehead of the former Judith Bridge. The centre of the Hospitallers was the Church of Our Lady beneath the Chain, whose name reflects the fact that a chain was used either to seal the gate of the commandry or to block boats on the river to prevent them from passing through Prague without paying customs duties.
The original church was built after 1158, when a commandry of the Order of Saint John of Jerusalem settled below the castle near Judith Bridge. The three-aisle Romanesque basilica was completed in 1182. After 1314, when the Order of Saint John of Jerusalem obtained funds by selling off the property of the defunct Knights Templar, the Romanesque church was knocked down and construction started on a grand Gothic three-aisle basilica that was likely carried out by Peter Parler’s workshop. Remnants from the older building have been preserved on the right-hand side of what is now the courtyard. Out of the original plans, only the choir and sacristy were built; the western prism tower was started but never completed. The church was rebuilt in Baroque style in the course of the 17th century. Most work was carried out by Carlo Lurago and stone mason Giovanni Battista Spinetti, and the appearance of the church has remained the same since.
A Baroque painting by Karel Škréta of the Madonna Blessing the Maltese Knights at the Battle of Lepanto (cca 1651) hangs at the main altar. Another painting by Škréta of the Beheading of Saint Barbara is at the southern side altar (1674). Most of the sculptures adorning the church were created by Jan Petr Wenda.
The origin of the name of the church refers to the former Judith Bridge and the chain on the bridge tower gate. Apparently, the chain was stretched from this site in the Lesser Town all the way across the Vltava River to the Old Town so as to prevent boats from passing though Prague without paying the toll.
The church belongs to the Czech Grand Priory of the Order of the Knights of Malta as a monastery church and is the property of the Sovereign Military Hospitaller Order of Saint John of Jerusalem of Rhodes and of Malta.
Source: https://www.prague.eu/en/object/places/462/church-of-our-lady-beneath-the-chain-kostel-panny-marie-pod-retezem