In Ohio, walls of only two large circular enclosures, High Bank Great Circle and Newark Observatory Circle, form a "very close approximation to a true circle" as surveyed by James Middleton in an 1882 survey for the Smithsonian (Thomas 1894). These are also the only circles connected to adjusted octagonal shapes (Greber and Horn 2010). Ongoing work has shown that High Bank Great Circle really is an Ohio Hopewell construction (Greber 1999, 2002, 2005a; Greber and Shane 2009).