It took Christian kingdoms over 770 years to retake the land they lost in a single decade

Muslim forces conquered most of the Iberian Peninsula between 711 and 718. Christian kingdoms spent the next seven and a half centuries clawing it back in stages, a process now called the Reconquista, finally completing it with the fall of Granada in 1492 — the same year Columbus sailed for the Americas.

— Wikipedia contributors, Reconquista — Encyclopedia entry