The Ancient Bridges on the via Annia in the Ca' Tron Estate (Venice, Italy)

In 1999 the University of Padua has begun a geoarchaelogical research in the area of the Ca’ Tron estate (Treviso), in the region of the ancient Venetian/Roman town Altinum by the inner shores of the lagoon of Venice. The research is carried out with a multidisciplinary approach, involving archaeologists, geologists, archaeometrists, paleobotanists, remote sensing specialists, geophysicists. The main archaeological features discovered in the study area are two branches of the Roman road via Annia: an older and outer one, nearer to the lagoon, and a more recent and inner one. Archaeological evidence in the estate spans since the Neolithic to Middle/Modern Age and some artefacts testify a millennial use of the road. The paper focuses on two bridges built along the two different branches of the road to cross an old river, now named “Cana palaeochannel”: a protohistoric bridge entirely made of wood and a stone-and-bricks Roman bridge with a wooden foundation. The preservation of the wooden structures allowed us to apply both radiocarbon and dendrochronology for absolute dating. The intervention so far conducted on the pre-Roman bridge had a preliminary character. The remains brought to light till now of what is thought to be a wooden bridge consist in two parallel rows of vertical posts and in a “U” shaped structure made of three huge horizontal beams, which were dated in the ranges of 12th – 11th and 8th - 6th centuries cal BC, according to radiocarbon determinations. The stone-and-bricks Roman bridge was built along the inner route, where an extensive excavation and a complete data collection were made. An extensive sampling was also carried out on the wooden foundations, made of over 560 posts, allowing to recognize the exclusive use of oak trees in preparing the structure. Dendrochronology assesses one single felling phase: the analysed samples come from trees cut in the same season in the same year. The dendrochronological sequence was absolute dated by using the ‘wiggle-matching’ method, with the last ring dated in the range between the last decades of the 1st century cal BC and the first years of the 1 century cal AD, during the age of Augustus.A reconstruction of the Roman bridge based on the preserved remains will be proposed too, in order to put it at the right place in history of Roman bridge engineering.