In the second year of Thutmose's reign, a stele at Tombos records that he built a fortress there. This is near the third cataract. Before this the Egyptian army had stopped at Buhen, at the second cataract. This stele says that he already fought in Syria. His Syrian campaign may be placed at the beginning of the second year of his rule. The Syrian campaign was the farthest north any Egyptian ruler had ever campaigned. Although it has not been found in modern times, he set up a stele when he crossed the Euphrates River. During this campaign, the Syrian princes declared loyalty to Thutmose. However, after he went back to Egypt, they stopped tribute and began building defences against future attacks. Thutmose celebrated his victories with an elephant hunt in the area of Niy, near Apamea in Syria. He returned to Egypt with strange tales of the Euphrates, "that inverted water which flows upstream when it ought to be flowing downstream." The Euphrates was the first major river which the Egyptians had seen which flowed from the north. This would be downstream on the Nile, instead of the south which was upstream on the Nile. The river became known in Egypt as the "inverted water."