Shame the flan's a bit small and the inscription is partially off the flan on both sides. Nonetheless, enough remains to make an exact attribution of the coin. It's a new purchase and I like the collection of ligatures in the inscription. Note the N+E ligature in the obverse inscription, the O+V (ȣ) ligatures and the A+P ligature in the reverse inscription. The reverse inscriptions on coins of Marcianopolis (and of Moesia Inferior in general) often have the name of a consul (a.k.a. legate, consular legate) or governor under whose authority it was issued. This information can help with dating a coin. Not in this case, though. According to Hristova & Jekov, Julius Antonius Seleucus was legate from AD 218-222, virtually the entire reign of Elagabalus. A good page to determine the Roman Legates from Moesia Inferior is by Akropolis Ancient Coins. The VΠ before their name is their title, an abbreviation for ὑπατεύοντος, the masculine genitive singular participle of the verb, ὑπατεύω, meaning "to be consul" (the Greek word is translated into contemporary Latin inscriptions as consularis). Occasionally, the abbreviation ΗΓ is used, an abbreviation for the noun ἡγεμόνος, the genitive masculine singular of ἡγεμών, meaning "governor." Elagabalus, AD 218-222 Roman provincial tetrassarion, 8.53 g, 24.2 mm, 7 h Moesia Inferior, Marcianopolis, Legate Julius Antonius Seleucus, AD 218-222 Obv: ΑVΤ Κ Μ ΑVΡ ΑΝΤΩΝΕΙΝΟC, laureate head, right Rev: VΠ Ιȣ ΑΝΤ CΕΛΕVΚȣ ΜΑΡΚΙΑΝΟΠΟΛΕΙΤΩΝ, Homonoia standing left, holding patera and cornucopiae. Refs: BMC 3.34, 47; AMNG (Pick) 856; Moushmov 633 Post anything you feel is relevant, of course.
My similar coin shows Elagabalus and Julia Maesa and a minor variation of the reverse legend. It uses first Iȣ as does your but the second time the same letters came up, they are spelled out CΕΛΕVΚOV. Another reverse type here used the OV both times but had to get creative at the end to fit in all the letters. Some coins would have continued the end in line but here the last letters were flipped in exergue ΛΙΤΩΝ, dropping the E and making ligate the ΩΝ. They did every die as it struck them at the time.
Cool coins. I like the green patina on Roman Collector's coin, and the graceful figure on the reverse of Doug's second. Here's my only Marcianopolis: Elagabalus and Julia Maesa. Moesia Inferior, Marcianopolis, minted under Legate (Governor) Julius Antonius Seleucus, ca. 220-221 CE. Æ Pentassarion (30mm, 13.57g, 12h). Julius Antonius Seleucus, legatus consularis. Æ27, 11.09g. Moushmov 682, Varbanov 1638 (R5), Zhekov/Jekov 6.28.39.1 (R6), P.R. 969, H.M. 682. Obv: AVT K M AVΡH ANTΩNEINOC AVΓ IOVΛIA MAICA AVΓ; laureate head of Elagabalus r., facing diademed and draped bust of Maesa l. Rx: VΠ • IOVΛ ANT • CEΛE – VKOV MAΡKIANOΠOΛI / TΩN in exergue; Liberalitas standing l., holding coin counter and cornucopia; in field r., Є. Very rare. VF. Die duplicate of an example found at https://sites.google.com/site/elagabaluscoins/ (author unidentified); however, the reverse type of that coin is misdescribed as Libertas, and the obverse head of Elagabalus is misdescribed as bust, draped and cuirassed.
