In Rome, state cult to a living emperor acknowledged his rule as divinely approved and constitutional. As princeps (first citizen) he must respect traditional Republican mores; given virtually monarchic powers, he must restrain them. He was not a living divus but father of his country (pater patriae), its pontifex maximus (greatest priest) and at least notionally, its leading Republican. When he died, his ascent to heaven, or his descent to join the dii manes was decided by a vote in the Senate. As a divus, he could receive much the same honours as any other state deity – libations of wine, garlands, incense, hymns and sacrificial oxen at games and festivals. What he did in return for these favours is unknown, but literary hints and the later adoption of divus as a title for Christian Saints suggest him as a heavenly intercessor. In Rome, official cult to a living emperor was directed to his genius; a small number refused this honour and there is no evidence of any emperor receiving more than that. In the crises leading up to the Dominate, Imperial titles and honours multiplied, reaching a peak under Diocletian. Emperors before him had attempted to guarantee traditional cults as the core of Roman identity and well-being; refusal of cult undermined the state and was treasonous.

What was the emperor's rule in Rome?