The controls were designed from the outset to minimise the chance of operator error and include a complete model of the locks, with moving components that mirror the state of the real lock gates and valves. In this way, the operator can see exactly what state the locks and water valves are in. Mechanical interlocks are built into the controls to make sure that no component can be moved while another is in an incorrect state—for example, opening the drain and filling the valves of a lock chamber simultaneously. Construction The construction of the locks began with the first concrete laid at Gatun, on August 24, 1909, by the Philadelphia-based company Day & Zimmermann (formerly known as Dodge & Day). The Gatun locks are built into a cut made in a hill bordering the lake, which required the excavation of of material, mostly rock. The locks themselves were made of of concrete. The quantity of material needed to construct the locks required extensive measures to be put in place to handle the stone and cement. Stone was brought from Portobelo to the Gatun locks, while the work on the Pacific side used stone quarried from Ancon Hill. Huge overhead cableways were constructed to transport concrete into the construction at Gatun. high towers were built on the banks of the canal, and cables of steel wire were strung between them to span the locks. Buckets running on these cables carried up to six tons of concrete at a time into the locks. Electric railways were constructed to take stone, sand, and cement from the docks to the concrete mixing machines, from where another electric railway carried two 6-ton buckets at a time to the cableways. The smaller constructions at Pedro Miguel and Miraflores used cranes and steam locomotives in a similar manner. The Pacific-side locks were finished first—the single flight at Pedro Miguel in 1911 and Miraflores in May 1913. The seagoing tug Gatun, an Atlantic entrance working tug used for hauling barges, made the first trial lockage of Gatun Locks on September 26, 1913. The lockage went perfectly, although all valves were controlled manually since the central control board was not yet ready. Map References Panama Canal Authority FAQ A History of the Panama Canal, from the Panama Canal Authority Cement And Concrete, from The Builders of the Panama Canal, CZ Brats The Panama Canal, by Colonel George W. Goethals