The term Umm an-Nar culture has been adopted to define the protohistoric assemblage unearthed for the first time in the early 1960s on the island of that name lying just off Abu Dhabi (Thorvildsen, 1962; Bibby, 1969:227–234). Over the past five years, as archaeological research has been promoted in the Sultanate of Oman, the term has often improperly been extended to cover any protohistoric site discovered in the southeastern corner of Arabia, thus becoming identified with practically all assemblages represented by Black-on-Red wares, cairn burials, tower-settlements, and mortarless stone masonry (Frifelt, 1975:57). Thus, the term, which originally well defined a highly aggregated cultural complex located in coastal Abu Dhabi, risks being diluted into a broad regional connotation applied to a very long period of time. By providing further data for the absolute chronology of the Umm an-Nar settlement, we intend here to suggest a tentative periodisation or sequential articulation for the 3rd millennium BC cultures of Oman, chronologically preceding it.