‘And the east border was the Salt Sea, even to the end of Jordan.'
The east border of Judah was simple. It went from below the Dead Sea and along its western side up to where the Jordan entered it. At the time that this was written the Sea probably extended a few miles further north. It is slowly getting smaller due to rapid evaporation.
Joshua 15:5-6 (5b-6)
‘And the border of the north quarter was from the bay of the sea at the end of Jordan. And the border went up to Beth-hoglah, and passed along by the north of Beth-arabah, and the border went up to the stone of Bohan the son of Reuben.'
We now trace the northern border westward. It begins at the northern tongue of the Dead Sea. Beth-hoglah was near Jericho (Joshua 18:21) and was a Benjamite city. It has been identified with the ruins of Kasr Hajleh, and is four kilometres (three miles) north of the present Dead Sea. Beth-arabah (‘house of the Arabah') was in the barren, rocky country between the Central Range and the Dead Sea, sometimes called Jeshimon (waste, desert) mentioned in 1 Samuel 23:19; 1 Samuel 23:24. In verse 61 it belongs to Judah. In Joshua 18:21 it is a Benjamite border town. As a border town it was probably shared between them, the boundary going through it. It would have lands at both sides, some allocated to one and some to the other.
“And the border went up to the stone of Bohan, the son of Reuben.” Compare Joshua 18:17. This was clearly an important recognised landmark. Bohen means ‘a thumb'. This may refer to a large stone shaped like a thumb, near to an eminence or larger rock called Reuben (not necessarily connected with the patriarch). It is alternatively possible that a famous man Bohan was buried there who was son to an unknown Reuben, or even that it commemorated some famous exploit by a Reubenite who had crossed the river with Joshua. But the impression is of an ancient landmark. The portion of the Biblical Reuben was across the river.