Qattara Depression, an arid desert basin in northwest Egypt, about 200 miles (320 km) west of Cairo. The depression is about 70 miles (110 km) wide and about 170 miles (270 km) long. The depression's soft sands make it impassable to vehicles. For this reason British forces made it the southern anchor for their line of defense during the Battle of El Alamein, one of the decisive battles of World War II.