An Historical Summary of Angelic Hierarchies from Part VII: The “Seven” Thrones in In Operibus Sigillo Dei Aemeth by David Richard Jones.
“St. Thomas Aquinas (c. 1225–1274) made the authoritative resolution of this dilemma and subsequently established standard Christian dogma in the first part of his Summa Theologica. He refers to the Thrones 15 times in question CVIII: ‘The angelic degrees of hierarchies and orders.'” [via]
St. Thomas Aquinas