Thomas aquinas wrote Summa Theologica as

The Summa Theologiæ (written 1265-1274 and also known as the Summa Theologica or simply the Summa) is the best-known work of Thomas Aquinas (c. 1225-1274). Although unfinished, the Summa is "one of the classics of the history of philosophy and one of the most influential works of Western literature."