Arab-Byzantine, a Byzantine Follis of Constans II, countermarked θC on reverse, 3.18g (Goodwin A7 var.). Host coin fair, countermark good fine, rare.
Reference: Goodwin, T., 'Countermarking in Seventh Century Syria, Part II: Countermarks from after the Arab Conquest', Supplement to ONS Newsletter 183, 2005
Estimate: £60-80