Hadrian's Wall: Geoblox offers a free download of a section of Hadrian's wall.
"At this scale, you will need 79 wall segments to make one Roman mile. To build the whole wall you would need 6400 models stretching 6/10 of a mile!" this picture shows one of the turrets although the free download is just the wall.
A book containing the complete wall along with other models from the ancient world for reproduction in the classroom is available for $26.