Mosta is a small but densely populated city in the Northern Region of Malta. The most prominent building in Mosta is the Rotunda, a large …Mosta is a small but densely populated city in the Northern Region of Malta. The most prominent building in Mosta is the Rotunda, a large basilica built by its parishioners' volunteer labour. It features the world's 3rd largest unsupported dome, and displays a replica of a German bombshell that famously crashed through the dome but did not detonate upon impact.