Ancient Assyria

Assyrians

Cecil Colwin writes in  Breakthrough Swimming (Human Kinetics, 2002 (available on Google Books as per link) : 

"In the ancient world, diverting rivers to protect city-states led to swimming for military purposes. Bas-reliefs housed in the British museum show a river-crossing by Assurnasir-pal, King of Assyria, and his army. When these reliefs were found in the ruins of the royal palace at Nimroud, students of swimming techniques were excited because here, at last, they expected to find evidence of swimming skills used in ancient times. Nineteenth-century observers thought the reliefs showed soldiers swimming either sidestroke or the trudgeon stroke, while 20th-century observers concluded that the Assyrians were actually swimming the crawl stroke! And so, as always, conclusions are drawn from one’s own vantage point. 

Above: Bas Relief of Assyrian army crossing river, from the British Museum.