From one my member :
Thermopyles
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Les Croisades
The Knights of Christ.
The never-ending source of reinforcements for the Frankish states of the Levant came from military orders. Directly dependent on the Pope, they had their own laws and became a powerful semi-independent military society in the Holy Land. They were also the most implacable enemies of the Muslims.
The main military orders, the Templars and the Knights of St. John of Jerusalem, called the Hospitallers were originally created to assist the pilgrims and treat the sick. These two orders, and some others, especially the Teutonic Knights, were initially organized as monasteries, their members being called "brothers." They transformed men religiously motivated into soldiers who became the main defenders of the Frankish states of the Levant.
While they retained their independence from the king and other princes, the military orders benefited from frequent donations of land and fortresses during the twelfth century, as well as legal and financial privileges. In 1244, the Hospitallers had 29 castles in the Holy Land; The Templars had nearly as much.
These encouragement were necessary to the Frankish states, for the kingdom was incapable of surviving without the orders and their military strength. These two orders, and some other smaller organizations, also had great possessions in Europe, given by grateful benefactors. All this assured them financial as well as political independence.
The Order of the Temple, the Templars was founded in 1115 by two knights who shared their horse in sign of poverty. Their aim was to protect the pilgrims who went to the Holy Land. Their image became the symbol of order. Originally known as "Poor Knights", their first installation in the temple of Solomon in Jerusalem gave them their name. The rule of the Templars reflected strictly that of the monks of Citeaux, the Cistercians, relying on the three vows of chastity, poverty and obedience.

Knights Templars.
The Templars quickly became recognized financial agents throughout Europe and the States of the Levant. Their role as bankers grew thanks to the unanimous recognition of their scrupulous honesty. But above all, their strict discipline, their courage and Christian fanaticism made the Templars one of the major pieces in the arsenal of the Crusades.
Decimated in Hattin.
At the battle of Hattin, the order was almost totally destroyed, and many castles fell into the hands of the Muslims in the months following the disaster. The order survived until the fourteenth century by managing its vast estates in Europe. But jealousy, both from ecclesiastics and lay people, caused him to be accused of all evil, a heresy as homosexuality, and Pope Clement V denounced it in 1307. The Templars were prosecuted, imprisoned, tortured, their lands and Their confiscated treasures.
The hospitallers bore the name of a Jerusalem hospital reserved for pilgrims before the first crusade. Following the capture of the city by the Crusaders, this hospital was entrusted to the Benedictines. In 1113, placed under the papal protection, its members formed the order of the Hôpital-de-Saint-Jean. In 1120, the order extended, taking charge of several hospitals through the Frankish states of the Levant.
Costume hospitalier knight late twelfth-early thirteenth
While the number of caregivers remained large, the order gradually took on a more warlike character. In 1136, it received the fortress of Gibelin (Jabalah), and its military evolution became more and more apparent during the XIIth century.
In 116, the term Chevalier de Saint-Jean fell into disuse and was replaced by that of Chevaliers Hospitaliers.At the battle of Hattin, they were recognized as completely military orders and in 1206, when they were still encountered in The hospitals, the organization of the knight brothers had become an independent military formation.
Although the military orders relocated to the Holy Land at the time of the Third Crusade, they were all weakened. Nor had they recovered the property they had before the catastrophic battle at Hattin where almost all the knights of the Frankish states had been killed.
In 1291, following the fall of Acre, the Hospitallers settled in Cyprus, then in Rhodes, becoming a naval power that ruled Malta until 1798.
The third order to intervene in the Holy Land was that of the Teutonic Knights, founded during the siege of Acre in 1189-1190 to cure the Germanic crusaders. He was recognized by the Pope in 1191 and became a military order seven years later. The Teutonic Knights, stationed in the north of the Free States of the Levant, suffered a severe defeat in 1210, prompting the surviving knights to come to Acre. The order had a significant number of castles but remained in the shadow of the Templars and the Hospitallers. However, when they were sent to the north of Europe to christianize the pagan tribes of Prussia and the Baltic countries, the knights turned into fanatical and merciless conquerors.

Chevaliers Teutoniques
Sources :
Atlas historique. Les Croisades de Angus Konstam.
Osprey armées et batailles. Les Croisés.
Liens web :
http://compagnonsdevalerien.bbactif.com/creation-de-costume-f8/costume-chev…