Educational toy made in plastic versions. In the mid-1950s, more explicitly engineering-themed construction toys appeared, including plastic girders, columns, and panels that could be assembled into a model curtain wall skyscraper. Later, this Girder and Panel structural system was extended to a Hydro-Dynamic setup by adding pipes, valves, tanks, nozzles, and pumps to allow construction of model plumbing, HVAC, and chemical engineering systems like a simulated distillation column. Other extensions of the system supported suburban-style housing developments (Build-A-Home), or monorail transportation systems (Skyrail). The building toy Lego was originally developed by Ole Kirk Christiansen in Billund, Denmark, in the 1930s. The name
History of Lego Duplo comes from the Latin word "duplus", which translates literally as double, meaning that a Duplo brick is exactly twice the dimension of a Lego building brick (2× height by 2× width by 2× depth = 8× the volume of a brick). During the last three decades of the 20th century Lego expanded into new areas of toy making and marketing. In 1971, Lego began to target girls by introducing furniture pieces and dollhouses. In 1972, Lego added boat and ship sets, with floating hull pieces. During this same period, Godtfred Kirk Christiansen's son, Kjeld Kirk Kristiansen, joined the managerial