The history of the motorcycle begins in the second half of the 19th century. Motorcycles are descended from the "safety bicycle," a bicycle with front and rear wheels of the same size and a pedal crank mechanism to drive the rear wheel. Despite some early landmarks in its development, the motorcycle lacks a rigid pedigree that can be traced back to a single idea or machine. Instead, the idea seems to have occurred to numerous engineers and inventors around Europe at around the same time.