Diocletian's groundbreaking reform was to split the Empire into four subunits, with the two co-Augustii assisted by the junior Caesars. Why did he do this? The conventional explanation is that, after the crises of the third century, the army and bureaucracy were drained. But why would this necessitate a four-way split? Most of all, why did Diocletian (who had risen from basically nothing, and so, presumably, would be loath to give power away) even agree to this scheme?