The Red Cross

The Red Cross: A History of the Knights Templar by Richard Baigent is a fictional book within Deus Ex.

Volume One: Defenders of the Faith
...Upon the deliverance of Jerusalem, the Holy Lands remained in a precarious state, surrounded on all sides by hostile Mohammedan neighbors. It was then that Hugues de Payens, a knight from Champagne, bound himself and eight fellow knights in a vow to forever protect the "Kingdom of Christendom." Accepted in 1118 by Baldwin II, the Patriarch of Jerusalem, they were given charitable lodgings in the city temple where they became the "pauvres chevaliers du temple," or the "poor knights of the temple." It was not until later at the Council of Troyes that the Templar Knights adopted the austere, monastic Rule of St. Benedict, along with the white garments of the Cistercians -- adding to them the characteristic red cross that symbolized their willingness to spill their own blood in the defense of the One True Faith. The Templars quickly became a popular order, renowned as "lions at war and lambs at the hearth." They were soon exempted by the popes from all secular and episcopal authority save that of the popes themselves, and their lands exempted from all taxation...

Volume Two: Lions of God
...and every sovereign of Europe made donations to the order, be it land, money, arms, or men. They triumphed in battle after battle, the first to attack and the last to retreat, "rough knights of the battlefield" as described by Jacques de Virty; if taken prisoner they refused all efforts to secure their freedom, instead becoming martyrs to the cause of God. With every success, the order prospered even further -- at their height they were said to have owned over 9000 estates throughout Britain, France, Italy, and the Holy Lands, including a network of castles and commanderies built to protect the frequent pilgrims to Jerusalem. In all but name, the Templars virtually ruled Jerusalem and -- in what can only be termed hubris -- recognized no temporal authority over their affairs save that of the Church. By 1250 the coffers of the order had grown so large that it was not uncommon for pilgrims to deposit their money with a temple in London or Paris, and then cash in their receipt upon arriving in Jerusalem, thus establishing the foundations for modern banking and checking accounts...

Volume Three: Fall of the Knights
...while many charges can be disputed, it is clear that the more the Knights prospered, the less they became the austere monastic order that had originally been envisioned by de Payens a century before. Eventually even excommunicated men and criminals were accepted -- as long as they pledged blind obedience to the order. Rumors of secret initiation rituals and the "osculum infame" ("infame kiss") flourished, as did stories that they worshipped Baphoment and other false pagan gods. But it was their rivalry with the Order of the Hospitalers and their continued arrogance that were most responsible for their downfall. When Jerusalem was finally lost to the mighty forces of Saladin, Philip the Fair saw an opportunity to bring the Templars to heel... and greatly expand his own holdings. With the cooperation of the French pope Clement V, Philip accused the Templars of heresy and in 1304 placed all members of the order in France under arrest, subsequently subjecting them to brutal interrogations in an effort to determine whether the rather fanciful charges of sodomy, apostasy, and devil worship were true...

Volume Four: Descent Into Shadows
...but despite Clement's later efforts to annul the proceedings, the confessions had become matters of record. Those who repented were spared the flames, while fifty knights who chose to recant their confessions -- becoming "relapsi," relapsed heretics -- were promptly burned at the stake. The remaining members of the order in France quickly admitted their guilt, and in 1311 an Apostolic Decree was issued dissolving the order. The Templar Knights had once been subject to no king or law; but in the end, they were swallowed by history. Many have debated whether the rather ignominibus dissolution of the order was entirely accidental, while some have even gone so far as to suggest that it was part of a larger plan on the Templar's part. Such a massive, powerful organization -- the argument goes -- could not have been brought so low, so easily. Obscure speculation concerning a mysterious hay wain that departed their commandery in Paris has led certain researchers to believe that they may have been protecting the secret of the Holy Grail, or the secret of transmutation, but still others contend that the Templar Knights merely went underground and founded the powerful, secretive banking societies of Switzerland...