Cirencester Wargames has a set of modifications for the popular Lion Rampant games to allow you to play games set in Early Imperial Rome.
Rules: Ancients
Historicon Ancients Rules
Historicon is a set of free wargames rules for ancients miniatures. Alienstar Games bills it as a return the ancients games of old, featuring lots of figures, buckets of dice and army lists.
Munera Sine Missione Gladiator Rules
Munera Sine Missione is a set of free wargames rules for gladiatorial combat. Author Alan Saunders writes that these are:
Gladiatorial combat rules, using a hex grid. Simple armour and weapon categories make it easy to use your favourite figures, whilst a single bout plays to a conclusion in less than 15 minutes, making it suitable for campaign play in an evening.
Hoplomachia Peloponnesian War Rules
Hoplomachia is a set of free wargames rules for the Peloponnesian War.
Heroes Before Iron Bronze Ages Skirmish Rules
Heroes Before Iron is a set of free wargames rules for skirmish games set in the bronze age.