This silver coin seems to be a fantasy or token minted along XV or XVI century. Was in an old bracelet with many other old coins.
Description of one sold on CNG given to me by an expert in a numismatic forum, but this one is one of 1/8 siliqua. No data about 1/2 siliqua coins.
CONSTANTINE V and POPE ZACHARIAS. 741-752 AD. AR 1/8 Siliqua . Rome mint. Crowned beardless facing bust, wearing chlamys; cross in left field / Rm monogram; Z (Zacharias) in upper left field. M.D. O'Hara and I. Vecchi, "A Find of Byzantine Silver from the Mint of Rome for the Period AD 641-752," SNR 64 (1985)This class was unknown before 1985 and is of considerable interest. Its existence shows that the silver coins at present listed in the various standard works under Constantine V for Rome, those with the reverse type K combined with a cross and emperor wearing a loros, must be re-attributed to Pope Constantine. Zacharias is also known to have issued square bronze tessere, cf. Berman pg. 31, 5. (NEW PARAGRAPH)Pope (and St.) Zacharias is noteworthy in history for his momentous decision to bless St. Boniface's anointment of Pepin the Short as king of the Franks. In 751, Zacharias appealed for the Franks' help against Aistulf, who had taken Ravenna and was demanding suzerainty over Rome as part of his enlarged dominion of the Lombards.
CONSTANTINE V and POPE ZACHARIAS. 741-752 AD. AR 1/8 Siliqua . Rome mint. Crowned beardless facing bust, wearing chlamys; cross in left field / Rm monogram; Z (Zacharias) in upper left field. M.D. O'Hara and I. Vecchi, "A Find of Byzantine Silver from the Mint of Rome for the Period AD 641-752," SNR 64 (1985) This class was unknown before 1985 and is of considerable interest. Its existence shows that the silver coins at present listed in the various standard works under Constantine V for Rome, those with the reverse type K combined with a cross and emperor wearing a loros, must be re-attributed to Pope Constantine. Zacharias is also known to have issued square bronze tessere, cf. Berman pg. 31, 5. (NEW PARAGRAPH)Pope (and St.) Zacharias is noteworthy in history for his momentous decision t