The Roman triumphal procession, like the ancient funeral with the coins over the eyes and bloodsoaked gladiatorial fights, are very powerful images in the modern imagination of the ancient world but are surprisingly slippery to pin down in reliable sourcing. To give an illustration of just how slippery it can be, Mary beard's The Roman Triumph is a 400+ page book dedicated entirely to tracking down where in the ancient source this modern image came from--the painted face, captives marched in chains, displays of booty, and a slave whispering "remember death"--and comes to the conclusion that there actually is not one. All of these are attested separately in one way or another ("remember death" comes from the early Christian author Tertullian), but the creation of a singular "Roman Triumph" with set elements is a modern one.

This does not mean that triumphal processions were not very important parts of a noble Romans career, but their specific form was not set. Arguably this is what made them so important--the ability of powerful leaders to shape the event to their own purposes.