As common with other churches from the same period, it is oriented east/west, with its façade facing a street which goes through the town of Krk in the north–south direction.

During several archeological excavations between 1956 and 1963 led by Andro Mohorovičić the ruins of an ancient Roman thermae dating from 1st century were discovered.

Large mosaic pieces worn out of people walking over them were found, which suggest that the site may have been used for Christian masses as early as the 4th century, before the cathedral was built.

According to historical records right next to the former tepidarium a Chapel of Saint John the Baptist with a baptismal font was later built, which stood there until 1565.

Beneath the floor of the present-day Chapel of the Holy Heart of Jesus a barrel-like piscina for baptismal water was also found.

Above the fourth interior capital (when counting from the south side entrance) there is an inscription dedicating the church to Virgin Mary, as it marks the place where the early Christian basilica used to end.