An ancient diocese of Emona was founded in 320 but in the seventh century the see was transferred on the coast of Istria in the city of Cittanova to form a new diocese.
From 811, the territory of the Ljubljana Archdiocese was part of the ecclesiastical territory of the Patriarch of Aquileia. Frederick III, Holy Roman Emperor, erected on 6 December 1461 the Diocese of Laibach, which was confirmed six months later, on 6 September 1462, by Pope Pius II.[6] Several days later, it was taken from the jurisdiction of the Patriarch of Aquileia and made directly subject to the Holy See. On 3 March 1787, it became an archdiocese and a metropolis, which it remained until 1807, when it was for political reasons degraded to a common diocese.[7]
The Nazi persecution of the Church in annexed Slovenia was akin to that which occurred in Poland. Within six weeks of the Nazi occupation, only 100 of the 831 priests in the Diocese of Maribor and part of the Diocese of Ljubljana remained free. Clergy were persecuted and sent to concentration camps, while religious orders had their properties seized.[8]