Anglo-Saxons were people of the sea and ships. So when a king died he was buried in a ship to take with him on his last journey.
Sometimes the king would be placed in a ship and the ship cast out to sea, but in other times a deep pit would be dug, a ship dragged from the sea and placed in the pit. The king and his goods would be placed in the ship and then everything would be covered over with soil to make a burial mound.
This is what happened at Sutton Hoo, Suffolk.