The Chronology of the Iron Age `Moats' of Northeast Thailand
McGRATH, R. J., Boyd, W. E., Antiquity
Since 1995, `The Origins of Angkor Archaeological Project' has been investigating the Iron Age occupation sites of the upper Mun River Valley in northeast Thailand (Higham 2000). These sites are characterized as mounds of accumulated occupation debris, encircled by earthwork features, commonly referred to as `moats'. While the project was largely concerned with excavation of a sufficiently large area of the occupation mounds to illuminate the prehistoric culture on the eve of the transition to statehood (Higham & Thosarat 2000), geoarchaeological research has addressed issues of site location within the landscape and geomorphological evolution (Boyd et al. 1999a; 1999b). This paper reports the complete chronometric data set for the moated features, focusing on Atomic Mass Spectrometery (AMS) radiocarbon and Thermoluminescence (TL) dating of materials recovered from the moats and related features described previously by Boyd et al. (1999b). This represents the first substantial body of data regarding the ages of these Iron Age features.
Background on the `moated' form
Higham (1996a: 211) has described the moated sites on the Khorat Plateau as `enigmatic'. The sites were identified by Williams-Hunt (1950) as having a limited distribution in the Khorat Plateau region. Although the existence of such sites was already known, Williams-Hunt was the first to note the significance of `a compact group of irregular earthworks which appear to pre-date the much publicized works of the Khmer empire' (Williams-Hunt 1950: 32). Although Williams-Hunt (1950) refers to the sites as irregular earthworks, importantly he also described the surrounding structures as `ramparts' and `moats'. These terms have implied a distinctly defensive role to the earthworks and, indeed, most subsequent investigators who have investigated the sites commonly referred to them as moated sites (Boyd et al. 1999a).
Quaritch-Wales (1957) was the first to follow Williams-Hunt's work with excavations at moated sites, and since then there have been many other studies (cf. Higham 1996a; 1996b). The concept of the `moat' has been most important, although little empirical investigation of these specific earthworks has been undertaken. Vallibhotama (1984), for example, suggested the moats were used for water storage, cultivation and defence, while Higham (1996b: 33) commented that `the purpose of the moats which ringed settlements far larger than their Neolithic or Bronze Age predecessors has been debated widely, with defence, agriculture and provision of domestic water prominent as possible explanations'. Moore (1988) postulated that the technique of moating sites had its roots in imitating the naturally-moated sites (i.e. areas of relatively high ground surrounded by rivers and/or swamp) occurring frequently on the floodplain. She, however, cautioned that the moats and earthworks of excavated moated sites had not been dated, but suggested a chronology spanning 1000 BC to 1000 AD for the moated form. Upon analysing 91 sites, Moore concluded that the preferred topographic location of the sites is on the low and upper terrace mounds at 130-180m altitude, adjacent to a watercourse that had been diverted to form an encircling moat; each site was unique in morphology due to the natural mound contours and local hydrology. Thus, the moated structures surrounding the mounds are seen as important water storage features in this dry region with potential irrigation prospects.
Following earlier inconclusive excavation of earthworks at two sites (Welch 1983), McNeill (1997) excavated the inner moat bank of the small upland site of Muang Phet, a site first excavated by Quaritch-Wales in the 1950s. Pottery sherds were recovered from within the bank, and importantly, for the first time, two radiocarbon dates were obtained from layers believed to pre-date (1710 [+ or -] 60 BP) and post-date (1640 [+ or -] 60 BP) the moats. The pot sherds and the dates led McNeill to conclude that the moats were constructed in the early centuries AD, although she pointed out these dates come from a single bank at one of many moated sites. …