Private schools ("public schools" in England and Wales), mainly attended by boys from the more affluent upper, upper-middle, and professional classes, are widely credited with three key achievements in the creation of modern codes of football. First, the evidence suggests that, during the 16th century, they transformed the popular, but violent and chaotic, "mob football" into organised team sports that were beneficial to schoolboys. Second, many early references to football in literature were recorded by people who had studied at these schools, showing they were familiar with the game. Finally, in the 19th century, former English public school boys, in a meeting organised by two old-boys of Shrewsbury, were the first to write down formal codes of rules in order to enable matches to be played between different schools. These versions of football rules were the basis of both the Cambridge Rules and the subsequent rules of association football, of which only one copy survives in the library of Shrewsbury.