The church was built on an islet called "Sa Illetta", quite close to the new canal harbour.  The islet used to be a port of call for the Phoenicians and the Romans, later becoming the capital of the Giudicato of Cagliari up until 1258, when it was destroyed by the Pisans.
The church is quite small and simple, its façade characterised by pastel yellow walls and a beautiful portal with an arch and a lunette, representing St. Simon who is blessing the lagoon and the fishermen.  Also to be mentioned is the short church tower and its bell with a "Tamil" language inscription, originating in south-eastern India.
Apparently, the little church dates back to a period between the sixteenth and the seventeenth-centuries, but the apse appears pre-Romanesque.
Nowadays, the church is privately owned and is open to the public only on the 28th of October.  On this occasion, the feast of St. Simon is celebrated, by the S. Gilla lagoon's fishermen, with the traditional cius procession.