The Israelis had constructed a series of fortifications along the canal called the Bar Lev Line, which was considered impregnable. The main obstacle of these defences was a massive artificial sand wall erected by Israeli engineers, high with a 45–60 degree incline, along the entire Suez Canal. The rampart were reinforced by concrete that also prevented any attempt by amphibious vehicles to climb the sand wall. To blast through the sand barrier the Israelis estimated would take at least twenty-four, probably forty-eight hours. Behind this rampart were a series of 22 fortifications comprising 35 strongpoints. On average, the fortifications were apart. A strongpoint was several stories deep into the sand and provided protection from a 1000-pound (~½ ton) bomb. Strongpoints incorporated trenches, barbed wire, minefields 200 meters deep, numerous bunkers and troop shelters, and firing positions for tanks. Each strongpoint had an underground reservoir filled with crude oil. The oil could be pumped into the Suez Canal via a pipe system, and ignited to create temperatures reaching . A second defensive line, behind the main line, was concentrated at likely crossing areas, and designed to be occupied by armored forces, incorporating tank firing positions. A third defensive line, behind the sand rampart, had its defences concentrated on the main roads and principal routes of advance for an attacker. Behind the main line on the canal were concentration areas for armor and infantry, supply depots, numerous artillery positions and so forth.