Microsoft is famous for their interview question, “why are manhole covers typically round?” While the question is asked to potential employees to discover their method of creative problem solving and ability to think on their feet, it’s true that manhole covers are typically round – for several reasons, including the fact that a round manhole cover cannot fall through a manhole, a round cover has a smaller surface thus needing less material in the casting process, and because the functionality is improved with the ability to be rolled, easily locked into place, and to stay flat under the presence of traffic and road movement. http://www.castagra.com/2013/08/creative-manhole-covers/