Which crusader victory in 1105 secured the northern borders of the Principality of Antioch?

The Crusader victory that secured the northern borders of the Principality of Antioch in 1105 was the Battle of Artah.

The battle took place on 20 April 1105 near Artah, east-northeast of Antioch. After the Crusader defeat at Harran in 1104, Antioch had abandoned several strongholds east of the Orontes River. Artah was especially important because it was the last Crusader-held fortress east of Antioch, and its loss would have exposed the principality's capital to direct pressure.

Tancred, acting as regent while Bohemond I was away in Europe, moved to recover the fortress. The ruler of Aleppo, Fakhr al-Mulk Ridwan, sent an army to oppose him. Tancred's smaller force defeated the larger Seljuk army, reportedly using the terrain and possibly a feigned retreat to disrupt the enemy infantry.

After the victory, Tancred recovered territory east of the Orontes and consolidated Antioch's frontier. Artah is therefore easy to confuse with Harran, a nearby major Crusader defeat, but the two battles had opposite outcomes: Harran weakened Antioch in 1104, while Artah helped restore its position in 1105.