Bus manufacture historically developed as chassis and body builds. Often, large bus operators or authorities would maintain separate stocks of bus bodies, and would routinely refurbish buses in a central works, and refurbished chassis might receive a different body. One of the first integral type bus designs combining the body and chassis was the Routemaster. In the 1980s, many minibuses were built by applying bus bodies to van chassis, so called 'van derived' buses. Many of these have been replaced by purpose built designs, although for smaller minibuses this is still an option.