An Investigation of Etruscan Cremations by Computed Tomography (CT)

Article excerpt

Introduction

In 2005-2006 the Soprintendenza for the Archaeological Heritage of Tuscany carried out an archaeological excavation in the 'Porta a Lucca' quarter of Pisa, where an important cremation cemetery was brought to light. Thirty-five funerary urns were documented, each deposited in a pit and covered with stones. Their morphology and ornament enabled the cemetery to be dated to the ninth to seventh century BC, corresponding to the Villanova culture (Paribeni et al. 2008). This important finding attests the Etruscan origins of Pisa, which, until now, had only been hypothesised on the basis of sporadic evidence.

The urns were removed from their pits, packed, and carried to the Laboratory of Palaeopathology at the University of Pisa for analysis. We performed a preliminary spiral Computed Tomography (CT) examination before proceeding to microstratigraphic excavation, in order to avoid inadvertent damage to the contents. From the CT datasets we were able to generate three-dimensional (3D) reconstructions, which allowed us to optimise the visualisation of the objects under examination, with the possibility of displaying them as 3D models, with varying degrees of opacity, or to virtually dissect them.

The use of CT in archaeology is not new: CT of mummified material was performed in 1976 in Toronto on the desiccated brain of a 3200 year-old Egyptian weaver, named Nakht (Lewin & Harwood-Nash 1977a & b). Also in the 1970s, whole-body imaging of another Egyptian mummy was performed (Harwood-Nash 1979). Although the Toronto researchers used a first-generation scanner, which enabled them to obtain only poor resolution images, they nonetheless became the first team in the world to perform a CT scan of a mummy and, with their pioneering studies, they opened up new opportunities to palaeoradiology. Since the 1970s, CT has been employed to investigate many other mummies, as well as skeletal remains (see bibliography in Chhem & Brothwell 2008). Recently, CT and micro-CT have been used on bioarchaeological materials, such as single human teeth and fossils (Hohenstein 2004; McErlain et al. 2004). However, only a single example of the application of CT to cremation urns is so far known: in 1995 five urns, found at Each End, Kent, UK, and dated to the Roman period (second century BC), were scanned by a second-generation scanner (Anderson & Fell 1995). The present study, to the best of our knowledge, is the first in which spiral CT has been used to investigate the content of the funerary urns of an entire cremation necropolis and to obtain 3D reconstructions.

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Results

A first group of eight urns were scanned by single-slice spiral CT (GE HiSpeed CT/i). A further 19 urns have so far been scanned using a more advanced multi-detector spiral CT (GE LightSpeed RT 16), which, in November 2007, replaced the old equipment as part of a routine technical upgrade (Figure 1). Scanning of the final eight urns is still in progress.

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Table 1 reports the averages of the acquisition parameters that emphasise the superiority of the multi-detector CT. The most relevant parameter is slice thickness, which determined the number of slices needed to cover the entire urn. The average number of slices rose from 72 (single-slice spiral CT) to 350 (multi-detector spiral CT). Voxel (volume element) size also varied accordingly: from 1.8[mm.sup.3] to 1.1[mm.sup.3], thus confirming the increase in spatial resolution allowed by multi-detector spiral CT.

The CT datasets were processed in order to obtain 3D reconstructions and complete virtual documentation of the urns and their contents. As such, it was possible to provide exhaustive, albeit preliminary, information concerning the quantity and disposition of the bone remains and the presence and position of metal objects within the urns. These metal objects are radio-opaque, thus making it possible to obtain easy identification and precise measurement of their dimensions and position (Figure 2). …