Charles Ellicott Commentary Genesis 14:10

"Now the vale of Siddim was full of slime pits; and the kings of Sodom and Gomorrah fled, and they fell there, and they that remained fled to the mountain." — Genesis 14:10 (ASV)

The vale of Siddim was full of slimepits. —That is, of holes from which bitumen had been excavated. Layers of this natural asphalt, well known both to the Greeks and Romans as pia Judaica, Judean pitch, still exist on the western side of the Dead Sea; and the places from which it had been dug out, and which are often very deep, formed dangerous impediments to the defeated side.