Ocmulgee Mounds are in present-day Macon, Georgia which I think is a key piece of information for this post. I recognize your original post is in reference to "the remains of a grandeur ancient capital", but my hunch is that there is a reason why shop was set up on this critical plot of Georgia land.
After a quick look this morning, maybe the information to the ruins of a "capital town" is in the below 1935 issue of The Georgia Historical Quarterly below.
Old Ocmulgee Fields - The capital Town of the Creek Confederacy
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Back to the idea of Macon's roots. Macon has some pretty insane architecture still standing today, with very little construction photographs available.
Municipal Auditorium
Built in 1925. The building is capped by a copper dome, claimed by locals to be the largest in the world, though difficult to verify.
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Hay House
Constructed from 1855 - 1859 "by some of the most skillful workers of the time", built in the Italian Renaissance Revival Style. 18,000sqft four-level mansion crowned by a two-story cupola.
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Armory Building
Constructed in 1884 in Victorian Architecture style with gothic towers and busts of Robert E Lee and Stonewall Jackson over the entrance.
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Saint Joseph's Catholic Church
Foundation laid in 1889 with the basement being used for services until 1903. The 3rd tallest building in Macon, at 200ft to the tip with an interior of 60 stained glass windows and an organ with 1,000 pipes.
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Old U.S. Post Office and Federal Building
Constructed in white marble from 1905 - 1908 in the Beaux-Art Classicism style with the post office on the first floor and judges' chambers on the second.
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Tarheel: This might not be much help, but I wanted to share some of the beautiful Macon architecture that still stands today. Thank you KD for the continued Georgia research. I always love reading your research and insights on my "old stomping grounds".