mediumaevum:

September 23rd

1122 –  Concordat of Worms, compromise arranged between Pope Calixtus II and the Holy Roman emperor Henry V, settling the Investiture Controversy, a struggle between the empire and the papacy over the control of church offices.  It has been interpreted as containing within itself the germ of nation-based sovereignty.

1338 – The English ship, Christofer went into battle at Arnemuiden armed with three cannons and one hand gun. This battle would be the first known time in history when a ship saw combat using artillery. This battle was also significant as the first naval battle of the Hundred Years War.

1459 – The Battle of Blore Heath, one of the first major battles in the English Wars of the Roses took place in  an area of barren an marshy moorland about two and a half miles from Market Drayton. At least 2,000 Lancastrians were killed, with the Yorkists losing nearly 1,000.