The Cathedral was built in the twelth century, in the Romanesque style. The arcades that span the aisles with the main nave are reminders of that period. At that time the church took the form of a three-aisle basilica. In 1430, it got the present presbytery, with a vestry and staircase tower; between 1455-1460 the groined vaulting in the side aisles was added, together with a choir enclosure. Aronud 1520, the main aisle of the church was vaulted, adding to its height. But, by that time, the church building already incororated some features that were not typically Gothic but rather characteristic of the Renaissance. In 1623 the church got its present bell tower, that was at the end of the eighteenth century struck by lightening and therefore its height was reduced to the present 57 metres. In 1969, the bell tower was renovated.
In the seventeenth and eighteenth centuries, the church was richly appointed in the Baroque style, thus obviating its Gothic features. The pulpit, rich with gilt ornaments, dates from the same period. In 1715, the St. Xavier Chapel at the southern and the Chapel of the Cross at the northern side were added. In 1771, the carved pews in the chancel with bassreliefs depiciting the scenes recorded to the Gospel According to St. John were decorated by the famous sculptor Josef Holzinger. He also carved the statues for the Chapel of the Cross. One of the valuablest examples of Gothic sculpting in Slovenia is the Statue of Madonna with The Child and can be found on Florian's alter.
The Cathedral's immediate surroundings - the oval, elevated terrace with small stone columns and pyramidal oak trees was designed by the great Slovene architect Joze Plecnik. At his direction, the tombstones (reminders of the old cementery just outdoor of the church reception area) were built into the outer Cathedral walls.