Development of an interdisciplinary approach to the radiocarbon dating of earth mortars from AlUla Old Town (Saudi Arabia). Integration of building archaeology, mortar analysis and radiocarbon dating

This paper discusses the approach used to identify the most relevant chronological information on the historic development of the abandoned site of AlUla Old Town, in the northwest of the Kingdom of Saudi Arabia (Western Asia). The approach is based on the use of the radiocarbon method to date earth mortar samples and soil layers used to create the constructive sequence of some buildings and, in turn, the chronological evolution of the site. Eleven samples of organic material (i.e., charcoal and vegetable fibres) were carefully removed from mortar samples and soil levels from six buildings and structures in the northern and southern areas of the town. Buildings and soil layers were chosen for their stratigraphic relevance and conservation conditions, based on an initial archaeological analysis of both buildings and underground structures. Laboratory-based mortar analysis led to the characterization of the mortar’s inorganic fraction and the isolation of the organic material for the radiocarbon dating. Results from the Accelerator Mass Spectrometry (AMS) laboratory provide evidence of a Late Mamluk/Early Ottoman constructive phase (i.e. 15th-17th c. AD) of the Old Town that was only partially known until very recently. Furthermore, the results allowed the identification of an Ottoman phase (i.e. 17th-19th c. AD) during which most of the buildings and structures were rebuilt, and of a Late Ottoman phase (i.e. 19th-20th c. AD) representing the most recent interventions before the end of the Ottoman occupation of the area.