Campus Martius was a defensive fortification at the Marietta, Ohio settlement, and was home to Rufus Putnam, Benjamin Tupper, Arthur St. Clair, and other pioneers from the Ohio Company of Associates during the Northwest Indian War. Major Anselm Tupper was commander of the Campus Martius during the war. Construction began in 1788 and was fully completed in 1791. The Campus Martius was located on the east side of the Muskingum River, and upriver from its confluence with the Ohio River. A firsthand description of the fort is provided in Hildreth's Pioneer History,
Campus Martius is the handsomest pile of buildings on this side of the Alleghany mountains, and in a few days will be the strongest fortification in the territory of the United States. It stands on the margin of the elevated plain on which are the remains of the ancient works [mounds], mentioned in my letter of May last, thirty feet above the high bank of the Muskingum, twenty-nine perches distant from the river, and two hundred and seventy-six from the Ohio. It consists of a regular square, having a block house at each angle, eighteen feet square on the ground, and two stories high; the upper story on the outside or face, jutting over the lower one, eighteen inches. These block houses serve as bastions to a regular fortification of four sides. The curtains are composed of dwelling houses two stories high, eighteen feet wide, and of different lengths.
The Campus Martius site is now occupied by the Campus Martius Museum. The Rufus Putnam House, part of the original Campus, is enclosed in the museum. Campus Martius was located around 39°25′17″N 81°27′40″W.