A place to collect medieval orbs that are divided into three sections (the basic shape of an inverted T inside an O)—cosmological, religious, philosopher's stone,e tc.
I'm adding some links to get it started, without commentary, because I haven't investigated this subject. Note that a few of these are conceptual rather than explicit inverted T-in-O, with labels rather than a line (e.g., leau et la terre):
Glass fragment 14th or 15th c Grimani Breviary c. 1490–1502 You are not allowed to view links.
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Login to view. 14th c BL Harley 334
Image Credit: numisantica.com See also p. 30 (sheep in orb)
Charlemagne w' orb (BL 15th c) Jerusalem inside orb, German c. 16th c You are not allowed to view links.
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These don't quite qualify, but may be related to some that do:
Von Bingen - divided into four Antwerp 1524 water/earth, cloudband, fire.
Ptolemy effect, sort of T-O-ish