209 FEATURE © Blackwell Publishing Ltd, The Geologists’ Association & The Geological Society of London, Geology Today, Vol. 26, No. 6, November–December 2010 Feature Debris flow burial of ancient wall system in the Upper Po River valley William C. Mahaney 1 , Pierre Tricart 2 , Rene W. Barendregt 3 , Christopher Carcaillet 4 , Davide Rabufetti 5 & Volli Kalm 6 1 Quaternary Surveys, 26 Thornhill Ave, Thornhill, Ontario, Canada, L4J 1J4 (arkose@rogers. com; b.kapran@hotmail. com), 2 Laboratoire de Géodynamique des Chaînes alpines, University of Grenoble, Observatoire des Sciences de l’Univers, 38041 Grenoble, France; (Pierre. Tricart@ujf-grenoble.fr), 3 Department of Geography, University of Lethbridge, Alberta, Canada, T1K 3M4; (Barendregt@uleth. ca), 4 Centre de Bio- Archéologie et d’Ecologie (UMR5059 CNRS/EPHE), Institut de Botanique, Université Montpellier 2, 163 Rue Broussonet, 34090 Montpellier, France; (Christopher.Carcaillet@ univ-montp2.fr), 5 ARPA Piemonte Area delle attività regionali per la previsione e il monitoraggio ambientale Via Pio VII, 9-10135 Torino, (d.rabufetti@arpa. piemonte.it), 6 Institute of Ecology and Earth Sciences, Tartu University, Tartu, Estonia, 51014. (Volli. kalm@ut.ee) The regrouping area, where Hannibal is thought to have reformed his army after forging a path through a massive rockfall in the Cottian Alps, has been reshaped by a blanket of sediment deposited from debris flows following heavy rain in spring, 2008. Analysis of precipitation data for the period mid- May to mid-June, 2008, shows that 722 mm of rain fell at 2150 m, falling off to half that amount at 3325 m on the flanks of Mon Viso. Following exhaustive analysis of environmental factors connected with the invasion of Italy at the start of the Second Punic War (218 bc), identification of the regrouping area for the Carthaginian Army centred on the presence of an ancient stone wall system which possibly dates from Hannibalic times. Lichen cover, lichen diameters, weathering characteristics, degree to which boulders had sunk into the resident soil, and presence of ancient hearths all combined to make this area a choice locale for reconstructive geoarchaeology. Large scale mass wasting off a prominent bedrock bar adjacent to the wall system in the Upper Po River Valley resulted in burial of most of the prominent wall structures which will complicate any exploration geoarchaeology attempts in future. A nested series of rock wall systems on the floodplain of the Upper Po River below the Col de la Traversette in the Cottian Alps of Italy were buried by debris flows emplaced during heavy spring runoff in 2008. Be- cause these interconnected wall systems are thought to date from Hannibal’s passage through the Alps, and may contain artefacts important in elucidating the military culture of ancient Carthage, burial may make it difficult to locate the sites for future geoar- chaeological excavation. The purpose of this article is to draw attention to the site, providing supporting geomorphological evidence as to its composition and age. The key environmental variables elucidated by researchers (whose work is indicated in the ‘Sug- gestions for Further Reading’, below), to identify the invasion route of the Punic Army, centre on: 1, pres- ence of a major defile in which the Gauls attacked; 2, presence of firnpack adjacent to the high col; 3, long view into Italy from the crest; 4, steep ledges and cliffs on the lee side of the Alps; 5, presence of a two-tier ‘landslide’ (rockfall) blocking the army on the lee side; and 6, a regrouping area sufficient to provide forage and water for the army. Many researchers have described various areas they consider suitable as the ‘regrouping or restaging area’, but with the exception of the Upper Po, all oth- er sites are below cols which lack: firnpack; sufficient view into Italy; and suitable blocking rockfall deposit. Only the regrouping area we described in 1988, with its ancient sunken wall system, closely fits the de- scription provided by Polybius (III, 55) who followed the path of the Punic Army some seventy years later. Because analysis of the walls and adjacent hearth sites might yield artefact information, important in elucidating information on the military culture of an- cient Carthage, it is important to document the effect of their burial by debris flow activity that occurred in late spring 2008. Shallow excavation that might have been possible following a metal detector survey