least one of the Roman emperors employed a slave to stand next to him at state functions and whisper into his ear “Remember, thou art mortal”
When a Roman General was awarded an official Triumph  they were accompanied in the ceremonial chariot by someone doing just that. Of course, when Rome became the Empire and the emperors gained executive and judicial powers they often awarded themselves a triumph and usually did away with the pesky slave.. Especially as most of the early emperors (pre-Constantine) regarded themselves as divine (and were usually deified after death  if power passed peacefully).
 There were fairly stringent requirements - one of which was that the General had to have had a successful campaign, returned victorious and provided plenty of loot and captives. The Senate were, at that point, the only body that could declare a Triumph. They could be anything from a simple procession where the general was dressed in a purple and gold toga (the colour of kingship and the colours of Jupiter) to a multi-day festival with arena games and feasting - paid for (mostly) by the general. In practice, a powerful and wealthy general was *far* more likely to be given a Triumph through back-room deals and bribery. Not much changes eh?
 The Empire had two rules in their conquered territories - they didn't care what the local religion was as long as it a) didn't practice human sacrifice  and b) was happy with the establishment and maintenance of local temples to worship deified emperors. Needless to say that Judea thoroughly trashed the second of those ideas.. And, with Christianity being formed, some of the outlier Romans saw the bread and wine as a ceremonial human sacrifice..
 The Druids being a prime example. They also, in the eyes of the Romans, committed two sins - human sacrifice and rallying the British against the Roman invaders.