Fourteen Mycenaean tombs have been excavated in 1962-63 next to the Hellenistic site of the Phocidian Medeon, which today lies on the Boeotian south coast. They belong to seven types: the pit, the simple cist made of upright slabs, th cist made of built-up walls, the rectangular built tomb with dromos, the L-shaped built tomb, the small tholos with stepped dromos and the standard tholos tomb - no rock-cut chamber tomb has been uncovered so far. Starting in LH IIA with built chamber tombs, both rectangular and L-shaped, the cemetery remained in use down to the end of LH IIIC. Although such an unusual diversity does call for an explanation, this paper is devoted exclusively to the built chamber tombs. It is suggested that the location of the site on two major routes of the Mycenaean period (both sea and land routes) might have contributed to an intermixing of populations and also to a high degree of diversification of the social hierarchy, the latter being reflected in the tomb type. The four relatively well-preserved built chamber tombs provide a good opportunity to define this less well-known type. They bring to light the roofing system combining corbelled walls with horizontal covering slabs on a rectangular plan. These features are considered to be distinctive of the built chamber tombs, unlike the dromos or the chamber for collective burials which are common to almost all Mycenaean tomb types. The type seems to be established by the end of LH IIA. It has obviously developed from the built cist during the Transition period (MH/LH) when tombs tended to become larger and richer. Their origin as well as other elements speak against the theory which considers them to be no more than a stone version of the rock-cut chamber tomb. However, it is questionnable whether the corbelled roofing is a local response to the need of reducing the span to be covered with slabs. There are EC forerunners on Syros but no missing links. The poor state of preservation of most of these built chamber tombs in Greece makes them difficult to identify but their distribution pattern appears to interest mainly the peripheric areas of Mycenaen Greece. Furthermore, the Medeon built chamber tombs display two exclusive peculiarities: the stepped dromos and the stomion opening at some height above the floor of the burial chamber. These features are best paralleled in the intramural family tombs of Ras Shamra-Ugarit on the Syrian coast, dating back to the end of MBA. In Ugarit, the above mentioned peculiarities appear to be dictated by the local architectural context. A case is made for Near Eastern influence in Medeon at the beginning of the LH II phase. Tomb Rho in Circle B at Mycenae also displays Ugaritic features at the same period. It is tentatively suggested that in both cases the tomb belonged to families of merchants involved in long-distance trade.