Legion was first conceived in August, 1993, but remained in a white paper and early design stage until 1996. During that time the fundamental Legion philosophy, object model, security model, run-time library architecture, program graph model, and high-level system architecture were designed and integrated. In that same period a prototype version of Legion, based on an earlier project -- Mentat -- was developed and used both as a proof-of-concept and a testbed for ideas in resource management, scheduling, autonomy, and so on. This early version of Legion, known as Mentat 3.0 with Legion extensions, is available for a wide variety of platforms.
In March, 1996, we began developing a "full-blown" version of Legion. The full-blown version differed from the Mentat-based version in several significant ways. Most importantly, it was a complete rewrite of the underlying run-time infrastructure, an implementation of the models described in the technical reports. We chose to do a complete rewrite rather than extensive modifications to the existing infrastructure for one primary reason: the original Mentat system was never designed to meet the new requirements. It could have been modified and then remodified, but the result would have possessed considerably less design and implementation integrity than a re-engineered run-time system.