This article presents a unique example of a roughly round ballista stone (ca. 32 x 31 cm) retrieved during excavations at Apollonia-Arsūf. It bears a two-line (one horizontal, the other vertical) Arabic inscription. Given the context of the ballista stones found at the site, it can be dated to March–April 1265, when the town and castle of Arsur were under siege by the Mamluk army headed by Baybars. The ballista stone is analyzed in relation to the site history and archaeology, its inscription, and the Mamluk sultanate 13th-century stone-throwing siege-machine artillery.