The magisterial palace in Senglea was built over a large cave that features a sculptured clam on its ceiling. The cave is located in Arches Street and it is also known as the Shell Fountain ‘l-Arzella’ since one finds a large clam carved in the rock. The cave is called ‘tas-Sirena’ as there is a legend tied to the place which says that during the Knights’ period, in this area people used to see a mermaid. It was thought that anyone tying his ship ‘underneath the mermaid’ would be blessed with luck. In Summer, boats sheltered in the cave and the garden were surrounded by a pergola that supported a canopy which was overflowed with vines. Today in the shell fountain, potable water still comes out of the rocks and the locals use this water for irrigation.