Summa Theologica

Summa Theologica is one of the two great works of Saint Thomas Aquinas, the greatest of the Scholastics.

The other one is the Summa Contra Gentiles.

The Summa Theologica is online at http://www.newadvent.org/summa ... to my knowledge, there isn't an online copy of Summa Contra Gentiles.

Thomas Aquinas was - and in my opinion still is - the pre-eminent Catholic theologian. If you've got a persona that would even be vaguely interested in such things, a brief look at the Summa Theologica on topics like Just War and Tournaments is probably in order.

Anyone interested in Knighthood (or for that matter, any of the Peerages) could in my view do worse than have a look through the Second Part of the Second Part of the Summa Theologica, and see what Thomas Aquinas had to say about various virtues and vices.