Wargames Rules For Classical Warfare is a set of free wargames rules by David Wareham. They are designed for playing games set in the period from c. 500 B.C. to c. 700 A.D. The rules use an alternate
movement system and whole figure casualty removal. They are primarily designed for use with 15 and 25mm figures.
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War Galley is a set of free wargames rules for ancient naval warfare. It very cleverly uses matchboxes and matchsticks for play.
Tom’s Ancient Warfare rules are a set of free wargames rules designed to be played with — of all things — Risk pieces. The author notes that the bases may need to be larger if you use historical miniatures.
The Die is Cast is a set of free wargames rules For The Battle of Pharsalus (48 BC), a decisive engagement between Caesar and Pompey.
The Portable Wargame: Ancients is a set of free wargames rules for ancients wargames using a gridded surface and individually based figures. The Ancients version is one of several using the same system in different periods.