Latrunculi or Roman Chess is mentioned in many ancient documents, but the rules are speculative at best. These rules are based on suggestions made by Dr. Wladyslaw J Kowalski, an engineering professor at Penn State University.
The folks from Board Games Studies take issue with Dr. Kowalski's suggestions. Their interpretation of the game is here. I chose Dr. Kowalski's version because, frankly, it looks more fun. Here are Dr. K's proposed rules.
Use a 12 x 8 board with the starting arrangement as shown below.
Black plays first (Black in this case is blue).
All pieces may move any number of spaces in the horizontal or vertical direction.
A single stone is captured if it is surrounded on two opposite sides.
The outside walls cannot be used to capture men.
A stone in the corner can be captured by two stones placed across the corner.
Multiple stones can be captured along a line.
The king (or dux) cannot be captured but can be immobilized by being surrounded on all four sides.
First player to immobilize the enemy king wins.
The king is immobilized if it is blocked by an enemy stone such that it has no place left to move.
If the game stalemates, the player with the most captured enemy stones wins.
Sequences of plays that repeat endlessly must be prohibited (this is usually obvious to both players after two series of moves repeats -- any move initiating a third repeating series of moves is illegal).
Players must announce when they 'squeeze' a stone in-between enemy stones (to avoid any later dispute).
Roman Chess board
More explanations later, but I wanted to get the basic board and rules up.