Antioch and the other Crusader States are constantly at war with the Muslim states of Northern Syria and the Jazeerah, principally Aleppo and Mosul.
After Ridwan of Aleppo died in 1113, there had been a period of a few years peace.
However, Roger of Salerno, ruling Antioch as regent for the child Bohemond II, had not taken advantage of Ridwan's death; likewise, Baldwin II, Count of Edessa, and Pons, Count of Tripoli, had looked after their own interests and had not allied with Roger against Aleppo, which had come under the rule of the Artuqid atabeg Ilghazi of Mardin in 1117.
The marriage of Pons to Cecile of France, the widow of his mentor Tancred, Prince of Galilee, and daughter of Philip I of France, had helped to reconcile the Norman and Provençal Crusaders, who had fallen out during the Siege of Antioch.
In 1118, Pons had allied with Baldwin II, newly crowned as king of Jerusalem.
Roger had captured Azaz in 1118, leaving Aleppo open to attack from the Crusaders; in response, Ilghazi invades the Principality in 1119.
Baldwin and Pons march north to aid Roger, who decides not to wait for them, and he and his army of seven hundred knights and three thousand foot soldiers, including five hundred Armenian cavalry, are slaughtered at the Battle of Ager Sanguinis; Roger is killed by a sword in the face at the foot of the great jeweled cross which had served as his standard.
The rest of the army is completely destroyed; only two knights survive.
One of them, Raynald Mazoir, takes refuge in the fort of Sarmada to wait for King Baldwin, but is soon taken captive by Ilghazi.
Among the other prisoners is likely Walter the Chancellor, who will later wrote an account of the battle.
The massacre leads to the name of the battle, ager sanguinis, Latin for "the field of blood."
The battle has proved that the Muslims can defeat a Crusader army without the help of the Seljuqs.
However, Ilghazi does not advance to Antioch, where Patriarch Bernard is organizing whatever defense he can.
Instead, llghazi is pushed back by Baldwin and Pons on August 14, and Baldwin assumes the regency of Antioch.
The defeat has left Antioch severely weakened, and subject to repeated attacks by the Muslims in the following decade.
As a result, the Principality will eventually come under the influence of Constantinople.
