Four columns formed part of a monument to a unique solution to the problem of ruling the Roman Empire; the Tetrarchy.

This institution was put into place by Diocletian in an attempt to formalise a method of succession that did not involve assassination. (The average reign of a Roman Emperor was 8 years 9 months). For further details about the "Crisis of Empire" click here. For a breakdown of the life expectancy of a Roman Emperor in greater detail, click here.

Diocletian split the empire into two. Each half would be ruled by an "Augustus" with a "Caesar" to be his successor when he voluntarily retired to private life. The system worked well with Diocletian in charge, but after his retirement it swiftly fell apart.