In the major port city of Patara on the southern coast of Roman Asia Minor, excavations unearthed a pharos (lighthouse) with an inscription that referred to an antipharos (a structure ‘opposite’ the lighthouse). It is unknown where the antipharos stood in Patara’s harbour, and scholars’ brief speculations about its location all assume that the antipharos was a second lighthouse. Yet a number of factors combine to suggest that there was only one pharos at Patara, including cautious Roman nocturnal sailing practices, the norm of single lighthouses in the ancient world, evidence of the pharos’ high visibility, and the only other instance of the word antipharos referring to something other than an operating lighthouse. Instead, the antipharos was probably either an unlit tower or a beacon instead of a lighthouse. I establish six possible locations for such an antipharos, and consider their likelihood based on how they might have ameliorated dangers to sailors entering the harbour. While there is not enough evidence to be completely confident, a rock islet that was in the middle of ancient Patara’s harbour emerges as the most probable location for the antipharos. The choice to build both a pharos and an antipharos, and where to place them, can illuminate the decision processes behind Roman harbour construction and the currently little-understood meaning of the word antipharos in antiquity.