The present parish church of Mosta is the second one to be built on the same spot. Before it the Mostin had already built a Latin-Cross shaped church as designed by the nineteen year old Tommaso Dingli. The old parish church started in 1610, took four years to complete and till 1682 to finalise its decoration. The locals could use this church as it fitted their needs along the 17th and 18th centuries. Yet, by the turn of the 19th century the population was showing unmistakable signs of a steady demographic increase. Thus Don Felice Calleja, parish priest of Mosta in 1820, felt the need to propose the building of a new parish church. After lengthy debate the proposal of Giorgio Grognet de Vassè was adopted. This was an innovative design for church architecture in Malta as it was based on an idea derived from Roman times – the Pantheon. Thus, on 30th May 1833, in the presence of the Governor of Malta, Frederick Cavendish Ponsonby, the first stone of the largest church ever built on these islands was laid.

To solve the problem of the site where the new church was to be located, Grognet came out with the idea that this second parish church would be located exactly on the spot of the first, yet without the Mostin having to find a substitute for the older church till the new Rotunda was completed. Therefore the proposal was that the second, larger and round temple would be built around the older church and the latter would only be demolished when the new building was ready. The idea was accepted and the locals, men, women and children gave their utmost not only in monetary contributions but also in labour. They toiled to build their new church seven days a week, including Sundays and feast days. In 1860, that is 27 years after the laying of the first stone, the church designed by Dingli began to be demolished.

Such a colossal work as the Rotunda naturally took a long time to complete and work continued so that the church would become what Grognet had designed. Thus, in 1909 the paving of the church in marble commenced and by 1930 the carving of the underside of the large dome had begun, taking about seven years to complete.

The parish church of Mosta, dedicated to the Assumption of Our Lady, is a majestic building which can hold about 12,000 people. It has many works of art by various artists including the titular painting attributed to Pasquale Buhagiar (1648-after 1698 ) and the original statue of the patron saint by Salvatore Dimech (1805-1887) with later major alterations by Censu Apap (1909- ).

Along its existence the Rotunda witnessed many events yet probably that of 9th April 1942 could have marked its total or partial destruction. This is due to an Axis bomb which pierced the dome without exploding. A monument to commemorate this event can be found in the Rotunda’s sacristy.