After the death of Alfonso VI of León and Castile, the Muslim inhabitants of Sintra, which was under Christian control, revolted in 1109.

The next year, 1110, saw the Almoravid leader, Syr ibn Abi Bakr, subduing the Muslim west of Andalusia.

[1][2] Seeing the Almoravid campaigning in Extremadura and fearing another rebellion, Count Henry sent troops to reinforce the garrison of Santarém in early 1110.

The Portuguese marched carelessly, encamped at a place called Vatalandi, and erected their tents to rest.

Knowing the Portuguese were small in numbers, they attacked and routed them, inflicting heavy casualties.