Spread over south-eastern Bulgaria, northern Greece and the European part of Turkey are a large number of megalithic tombs. These dolmens were built from around the twelfth century BC to about the sixth century BC. The monuments were built with well cut slabs, defining a rectangular space with a roof. A small hole marks the entrance. A dromos is also present in some dolmens and all of these structures used to be covered by a tumulus. We present the first results from a series of campaigns devoted to measuring the orientation of these structures. The first campaign was carried out in the Strandja Mountains where 31 dolmens (among other monuments) were measured. The dolmens are not orientated at random, and a particular pattern of orientation has been found for the entrance of these monuments. Several tentative explanations are attempted and supported with information provided by contemporary Greek sources.