The Chapters of Gallifrey — often called ruling Houses or colleges — were the Great Houses closest to the Lord President. (PROSE: Lungbarrow, The Book of the War, The Ancestor Cell) The High Council was composed of Cardinals elected from each Chapter, and (TV: The Invasion of Time) each Chapter was represented in the Time Lord Academy by a college bearing their name, (PROSE: The Ancestor Cell) such as the Prydonian Academy (PROSE: Timewyrm: Revelation) and the Academy of the Patrexes. (PROSE: Damaged Goods)
The ruling bloodlines often had sub-lines dedicated to exploring particular genetic philosophies. (PROSE: The Book of the War) The Doctor and Romana each belonged to both Prydonian Chapter (TV: Extremis, PROSE: Shada) and, respectively, Houses Lungbarrow and Heartshaven. (PROSE: Lungbarrow, AUDIO: Panacea) According to Commander Hallan, marriage was a way of strengthening the bonds between Houses and Chapters. (AUDIO: Spirit)
History
Each college was founded by one of the six legendary founders of Time Lord society (PROSE: The Ancestor Cell) who were present at the anchoring of the thread. (PROSE: The Book of the War) They included Rassilon, Omega, Pandak, Apeiron, and one other, as well as possibly Eutenoyar. (PROSE: The Infinity Doctors, The Ancestor Cell)
The most prominent of the original Chapters was the Prydonian Chapter, whose members included more Lord Presidents than any other Chapter. Its significance was closely followed by the Arcalian Chapter and the Patrex House. (TV: The Deadly Assassin) The Dromeian, Cerulean, (PROSE: Lungbarrow) and Scendeles Chapters were overshadowed by the others. (PROSE: The Ancestor Cell) These original ruling Houses were almost indistinguishable; The Book of the War said the members of all six were "equally pale and complacent". (PROSE: The Book of the War)
Two of the original ruling Houses, which The Book of the War called "House Ixion" and "House Catherion", began a slow decline after the anchoring of the thread and the ensuing Diaspora. They were eventually replaced by House Mirraflex and House Lineacrux. (PROSE: The Book of the War)
During the War in Heaven, political upheavals and social reforms on the Homeworld led to almost continual replacement of the ruling Houses as Newblood Houses were founded and other Houses rose and fell in importance. By the War's fifieth year, the six ruling Houses were the three traditional, political Houses Dvora, Tracolix, and Lineacrux, and the three military Houses Arpexia, Xianthellipse, and Mirraflex. (PROSE: The Book of the War)
Ceremonial colours
Each Chapter had its own dominant colour and wore robes of that colour during ceremonial occasions, such as the inauguration of a new Lord President. Prydonians used scarlet and orange; (TV: The Deadly Assassin) the secret minutes of House Dvora were kept in the records library's "Scarlet Chapterhouse" collection. (AUDIO: A Labyrinth of Histories)
The Scendeles ceremonial robes ranged from a light pink to a darker shade of red. (PROSE: The Ancestor Cell) The Arcalian Chapter used green and the Patrexians used heliotrope. (TV: The Deadly Assassin) Dromeians used silver-grey and Ceruleans, as their name would indicate, used blue. (PROSE: Lungbarrow)
Members of House Lineacrux wore yellow robes. (PROSE: The Brakespeare Voyage) The colour gold was reserved for the Gold Usher. (TV: The Deadly Assassin)