The Livonian Brothers of the Sword (latin Fratres militiae Christi), also known as the Christ Knights or The Militia of Christ of Livonia, was a military order started in 1202 by Albert von Buxhövden, bishop of Riga, and composed of German "warrior monks". It was primarly based on the rules of the Templars.
Since its founding, the order tended to ignore its supposed vassalage to the bishops. In 1218 the bishop asked for help from the Danish king, Valdemar II - but he instead made an agreement with the Sword Brothers order and conquered the north of Estonia.
The Sword brethren headquarters were at Viljandi (Fellin) in Estonia. The walls of the Grandmaster's castle are still standing. Other stongholds include: Wenden, Segewold and Ascheraden. The commanders of Viljandi (Fellin) Kuldiga (Goldingen), Aluksne (Marienburg), Tallinn and the bailiff of Paide (Järva) belonged to the 5-membered entourage of the Order's Grandmaster.
The Lithuanians beat the Brothers at the battle of Siauliai in 1236. They are reported as having suffered fifty deaths from amongst their ranks. Next year the order joined with the Teutonic Knights of Prussia, switching to their rules but maintaining administrative independence in their conquered lands. Between 1288 and 1290 they managed to conquer all of Courland and Livonia. In 1346 the united orders bought the rest of Estonia from Valdemar IV Atterdag, king of Denmark.
With the decline of the Teutonic Order by the middle of the fifteenth century, the Sword Brothers decided to resume their independence. In 1557 the Polish king Sigismund II Augustus intervened in a war between the bishop of Riga and the Brothers. After an agreement with the king, the last grandmaster of the order, Gotthard Kettler secularized the order, and converted to the Lutheran Church. In the south part of the Brothers' lands he created a Duchy of Courland and Semigalia. Most of the other lands were seized by Poland-Lithuania. The north of Estonia was taken back by Denmark and Sweden.