Valley of Siddim in the Old Testament
The Valley of Siddim is mentioned in Genesis 14:3-10. Gesenius from the Arabic explains "a plain (`eemeq) cut up by stony channels, which render it difficult of transit." `eemeq means a broad flat tract between hills, a suitable battle field for the four kings against five.
It had many bitumen pits. Onkelos, Aquila, and Rashi make Siddim plural of sadeh, "a plain." So Stanley "the valley of (cultivated) fields." Aben Ezra derives Siddim from sid, "lime," bitumen being used for lime (Gen. 14:3).
The words "which is the Salt Sea" imply that the Dead Sea in part now covers (probably at its Siddim end which is shallow and with shores incrusted with salt and bitumen) the vale of Siddim.
The plain is in part enclosed between the southern end of the lake and the heights which terminate the Ghor and commence the wady Arabah. In the drains of the Sabkhah are Gesenius' impassable channels.
The form of the plain agrees with the idea of an `eemeq. The Imperial Bible Dictionary makes Siddim a Hamitic word occurring in Egyptian monuments, the Shet-ta-n or land of "Sheth," part of the Rephaim who possessed that part of Palestine.
International Standard Bible Encyclopedia, which is in the public domain (with minor edits).