The locks on the Panama Canal are some of the most ambitious in the world, lifting and lowering ships across six steps (three up and three down), totalling 26 metres (85 feet) of elevation. The lock chambers are made from concrete, and measure a huge 33.5 x 305 metres (110 x 1,000 feet) in area. The walls are over 14 metres (45 feet) thick at the base, where water pressures are at their highest, but much thinner at the top, measuring 2.4 metres (eight feet). The chambers have a capacity of 101 million litres (26.7 million gallons) and a series of culverts are used to move water in and out. When the lock needs to be raised, water is brought in from the lake, and when it needs to be emptied, water is drained into the sea. Given the high quantities of water, the gates were engineered to be extremely strong, using the same chevron shape to hold the gates closed under the pressure of the water.