Iapetus is a strange Moon with a arrow-straight, 12-mile-high and 12 miles wide “wall” which precisely bisects the leading hemisphere over 800 miles in length. On the surface of Iapetus; the existence of thousands of square miles of clearly rectilinear ruins most now without roofs, but with ample surviving walls and an unnatural “tower-like structure,” rising more than a mile above the surrounding terrain... suggests that Iapetus could be a manufactured artifact.
Donald Goldsmith and Tobias Owen wrote of Iapetus in ‘The Search for Life in the Universe’ (1980):
This unusual moon is the only object in the Solar System which we might seriously regard as an alien signpost - a natural object deliberately modified by an advanced civilization to attract our attention.
Above text is an extract from Richard C. Hoagland’s in-depth analysis on this strange Moon Iapetus. The full story can be read at: http://www.enterprisemission.com/moon1.htm