Complex sentence: The battle was fought on 15 November 655, near the Winwæd, an unidentified river, where the Northumbrians were victorious and many of the Mercians and their allies were killed or drowned.
Split into simpler sentences: The battle was fought on 15 November 655, near the Winwæd, an unidentified river. The Northumbrians were victorious and many of the Mercians and their allies were killed or drowned.