The study of orientations is a key ingredient in most archaeoastronomical research. Typically, a number of synchronistic monuments belonging to a given culture or cultural horizon are measured and studied in order to see if they share a similar orientation. If an astronomical orientation appears, we may apply other archaeoastronomical procedures to justify further conclusions.

On a few occasions we perform studies that compare, for a given site, monuments of different periods. At most two or three periods are usually compared to verify persistence or to check for evolution in customs of orientation. We argue here that it would also be interesting to study orientations from a diachronic point of view, in order to investigate the persistence/evolution of this particular conception of space through time.

Mérida (Extremadura, Spain) and the neighbouring areas present a rich and highly interesting monumental heritage spanning from the Neolithic to the present, with monuments belonging to several different periods and cultures.

In the present study we will review the orientation of the monuments in that area. We will present some conclusions on the evolution/persistence of customs of orientation and value the applicability of this method to other areas.