Their southern border began at the tip of the Dead Sea on the south bay

The LORD will divide the Gulf of Suez. He will wave His hand over the Euphrates with His mighty wind and will split it into seven streams, letting people walk through on foot.

and the water flowing downstream stood still, rising up [in] a mass that extended as far as Adam, a city next to Zarethan. The water flowing downstream into the Sea of the Arabah (the Dead Sea) was completely cut off, and the people crossed opposite Jericho.

the Arabah east of the Sea of Chinnereth to the Sea of the Arabah (that is, the Dead Sea), eastward through Beth-jeshimoth and southward below the slopes of Pisgah.

All of these came as allies to the Valley of Siddim (that is, the Dead Sea).

He overthrew these cities, the entire plain, all the inhabitants of the cities, and whatever grew on the ground.

Your southern side will be from the Wilderness of Zin along the boundary of Edom. Your southern border on the east will begin at the east end of the Dead Sea.

The Arabah and Jordan are also borders from Chinnereth as far as the Sea of the Arabah, the Dead Sea, under the slopes of Pisgah on the east.