In this paper, we report on three areas of the Iberian Peninsula that were occupied at least during the Iron Age and the early stages of Romanisation, where observations of astronomical phenomena in the landscape, rock carvings, and Latin inscriptions point to a particular method of time reckoning. All of these sites have previously been connected with the Celtic culture. The knowledge of the natural world that Classical sources assigned to these peoples need not have been reflected in a monolithic calendrical system used by all Celtic communities on the Continent. In fact, such a ‘Celtic calendar’ may have had different expressions in different areas, expressed in different ways, although sharing some common characteristics such as the particual use of the lunar and solar cycles.