The first church — also consecrated to St. Vitus — that stood at the location of the present-day cathedral was an early romanesque rotunda founded by Wenceslaus I, Duke of Bohemia in 925. This patron saint was chosen because Wenceslaus had acquired a holy relic — the arm of St. Vitus — from Emperor Henry I. It is also possible that Wenceslaus, wanting to convert his subjects to Christianity more easily, chose a saint whose name sounds very much like the name of Slavic solar deity Svantevit. Two religious populations, the increasing Christian and decreasing pagan community, lived simultaneously in Prague castle at least until the 11th century.

In the year 1060, as the bishopric of Prague was founded, prince Spythinev II embarked on building a more spacious church, as it became clear the existing rotunda was too small to accommodate the faithful. A much larger and more representative romanesque basilica was built in its spot. Though still not completely reconstructed, most experts agree it was a triple-aisled basilica with two choirs and a pair of towers connected to the western transept. The design of the cathedral nods to Romanesque architecture of the Holy Roman Empire, most notably to the abbey church in Hildesheim and the Speyer Cathedral. The southern apse of the rotunda was incorporated into the eastern transept of the new church because it housed the tomb of St. Wenceslaus, who had by now become the patron saint of the Czech princes. A bishop’s mansion was also built south of the new church, and was considerably enlarged and extended in the mid 12th-century.