Exodus 14:3

They are entangled ... - The original intention of Moses was to go toward Palestine by the wilderness: when that purpose was changed by God’s direction and they moved southwards, Pharaoh, on receiving information, was of course aware that they were completely shut in, since the waters of the Red Sea then extended to the Bitter Lakes. It is known that the Red Sea at some remote period extended considerably further toward the north than it does at present. In the time of Moses the water north of Kolsum joined the Bitter Lakes, though at present the constant accumulation of sand has covered the intervening space to the extent of 8000 to 10,000 yards.