After spreading throughout Europe, Celts had been threatening Macedon and northern Greek states for years when a Celtic leader decided to invade. And just as the Spartans had done in 480 BC, a coalition of Greeks marched to meet them at Thermopylae. The ancient pass would once again be the site of a battle for the future of Greece.
The Reconquista, or Christian reconquest of Iberia, took nearly 800 years. The fighting did not come without great attempts by Muslim powers across the strait trying to reestablish their presence in mainland Europe. The last gasp of that effort came in the 1330s, when the powerful Marinid sultanate of what is modern Morocco invaded in an attempt to reverse Christian gains and secure the perilous position of the Sultanate of Granada.