Dating earthquake geological effects associated with historical earthquakes gives us relevant information for estimating the seismic acceleration value experienced in the ground. Historical manuscripts describing earthquakes and its effects help to assign a seismic intensity about the ground motion. In this context, lichenometry represents a good semi-quantitative method for dating exposed rock surfaces related to earthquake phenomena. In this work, we have carried out a lichenometry analysis for dating a large rockfall located 700 km from the epicentre of the Great Lisbon Earthquake, which occurred in 1755 CE and which was probably triggered by the surface shaking, according to the historical transcripts. A rock mobilization of about 2300 m 3 was caused by the earthquake, the largest historical earthquake affecting Western Europe (estimated magnitude of M 8.5, and close to 100,000 fatalities). The macroseismic intensity of the geological and environmental effects ESI07 estimated ranges between VI and VII, in contrast to the attributed European Macroseismic scale EMS98 of V from other studies. The EMS98 estimation was derived from a contemporaneous document of 1756 CE, describing the earthquake effects in buildings and environmental effects throughout the entire Kingdom of Spain. Aspicilia radiosa was used as the lichen species for dating purposes, and the annual growth-curve was estimated as 0.25 mm/yr as a linear growth rate. The resulting age for 19 analyzed blocks was 1733 CE, for the oldest lichen measured on the block side related to the broken-face. The error was estimated in 33 years based upon the comparison between the observed thalli and the calculated values from the linear fitting. The delayed time for lichen colonization was not estimated. Other error sources as lichen mortality, coalescence of thallus could ex- plain the deviation between the resulting lichen age and the earthquake occurrence.