MUD1 (referred to as MUD1, to distinguish from its successor, MUD2) is the oldest virtual world in existence. It was created in 1978 by Roy Trubshaw at Essex University on a DEC PDP-10 in the UK, using the MACRO-10 assembly language. He named the game Multi-User Dungeon, in tribute to the Dungeon variant of Zork, which Trubshaw had greatly enjoyed playing. Zork in turn was inspired by an older text-adventure game known as Colossal Cave Adventure or ADVENT. In 1985 Richard Bartle created MUD1 version 4, better known as MUD2. It was intended to be run as a service for British Telecom.