The Knights Templar and The crusades.

Mr Quint

I'm currently around quarter of the way through The Holy Blood and The Holy Grail. What a brilliant book, it really has it's claws in me.

thariq

You could also try the knights of black and white by Jack Whyte

Olly13

Piers Paul Read is good, my favourite is Dungeon, Fire and Sword by John J Robinson:

Dungeon, Fire and Sword: The Knights Templar in the Crusades by John J. Robinson Dungeon, Fire and Sword: The Knights Templar in the Crusades: Amazon.co.uk: John J. Robinson: Books