In this work we conduct a study of the orientations of 12 megalithic enclosures in the Alentejo (southern Portugal). Some of these sites date back to the sixth or fifth millennia B.C., and so are among the oldest stone enclosures in Europe. The results of the survey show a pattern of easterly (rising) orientations. In particular, we relate our results to previous studies by Michael Hoskin and colleagues, on the orientations of the seven-stone dolmens in this area, which have shown the existence of a possible sun rising orientation custom.