Roman Catholic Diocese of Civitavecchia-Tarquinia Tags: Clerical Administrative Region, Diocese.The Italian Catholic Diocese of Civitavecchia-Tarquinia (Latin: Dioecesis Centumcellarum-Tarquiniensis) is in Lazio and has existed under this name since 1986. The diocese is directly subject to the Holy See. thumbnail area (km2) 8.76e+08 country Italy Established 20 December 1825 Learn more... Loading...