The Battle of Simancas was a military battle that started on July 19, 939 in the Iberian Peninsula between the troops of the Christian king Ramiro II of León and Muslim caliph Abd-ar-Rahman III near the walls of the city of Simancas. The battle decided the control of the lands of the Duero.

The battle unfolded after the army of Abd al-Rahman III launched towards the northern Christian territories in 934. Abd al-Rahman III had gathered a large army of Moorish fighters, with the help of the Moorish Governor of Zaragoza, Abu Yahya. The Christian King Ramiro II, led the counter attack with an army constituted of his own troops, those of the Count Fernan Gonzalez, the Navarreses under García Sánchez I, the Kingdom of Galicia and the Kingdom of Asturias.

Arab witnesses chronicle a spectacular eclipse of the sun that took place on the first day of the battle:

As the army arrived near Simancas, there was an awful eclipse of the sun that covered the earth of a dark yellow amid the day and it filled us and the infidels with terror as neither had seen in their life such a thing as this. Two days passed without either side making any movement.^{[citation needed]}

The battle lasted some days with the Christian troops emerging victorious and routing the Moorish forces.

Coordinates: 41°36′00″N 4°49′01″W / 41.600°N 4.817°W / 41.600; -4.817