Game concept
Grand Cathedral
The game also links it as Grand Cathedrals.
From the game's encyclopedia
A Grand Cathedral is a Great Building raised through a Great Project in the capital of an Archdiocese, the seat of its Archbishop.
Raising the first Cathedral is a monumental act of devotion: its founder gains lasting Piety, Legitimacy and Spiritual Fulfillment, an additional Personal Tenet slot, and a standing bonus to their same-Faith Opinion. Once raised, it draws Christian pilgrims from across Christendom, expands the holder's Cathedral Complex, and may later be enlarged into a Gothic Grand Cathedral or Flamboyant Grand Cathedral.
The game's text for patch 1.20.1.2. Words in blue are entries of the encyclopedia: hover one to read it, as in the game.
Grand Cathedral is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "A Grand Cathedral is a Great Building raised through a Great Project in the capital of an Archdiocese, the seat of its Archbishop." It is part of Faith. The game also links it as Grand Cathedrals. Patch 1.20.1.2, from game/common/game_concepts/pam_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/pam_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.