Nauta is a set of free miniature wargames rules for playing out ancient naval battles. The files are hosted here:
Delta 7 Studios has a collection of free paper models of the Seven Wonders of the Ancient World: the Great Pyramid of Giza, Hanging Gardens of Babylon, Temple of Artemis, Statue of Zeus at Olympia, Mausoleum of Maussollos, Colossus of Rhodes and the Lighthouse of Alexandria.
Castle Cracker is a set of free wargames rules for backyard games in the ancient and medieval eras.
Roar of the Crowd is a set of free rules for playing science fiction, fantasy or historical gladiator games.
Here’s a tutorial for making a tower/obelisk such as those you might find in ancient middle eastern towns.