Nuno Álvares Pereira had been chosen to protect the frontier in this area, amid fear that a Castilian force could enter Portugal here.

The Castilian army consisted of some 5,000 men, mostly cavalry, which was besieging the village of Fronteira.

In the short battle that followed, the Castilian cavalry was unable to break the Portuguese formation, suffering heavy losses.

The battle of Atoleiros represents the first effective use of “square tactics” on the battleground.

This tactic, in which groups of infantry armed with both missile and hand-to-hand weapons defended themselves from all directions, was so successful that it was still in use over 500 years later during the Napoleonic Wars against mass French cavalry attacks, and during the Zulu War against huge masses of predominantly spear-armed infantry.