The Lotus X was an evolution of the first of Colin Chapman's fully enclosed aerodynamic designs: the Lotus Mark VIII and Mark IX. Featuring a spaceframe and described in its days as the "most nearly perfect sports car chassis", the Mark VIII was an extremely light and impressive race car. The Mark IX that followed was very similar but with a few improvements,  and the Mark X was the final iteration of that initial design, but featured a much more powerful Bristol 2L engine. It is thought that only 6 or 7 Mark X cars were built, even though these are the direct descendants of the better-known and more successful Lotus Eleven, which started to be built in 1956.