The wooden foundations of Rialto Bridge (Ponte di Rialto) in Venice: Technological characterisation and dating

The wooden foundations of Ponte di Rialto (Rialto Bridge), the oldest and most famous of the four bridges spanning the Grand Canal in Venice, Italy, were analysed in order to determine the tree species used to construct the foundation, to examine the timber's present-day physical and mechanical properties and to identify construction periods. The material recovered during geotechnical surveys underwent micro-morphological, physical, chemical and mechanical analyses. The radiocarbon method was used for dating purposes. The footings of the bridge's foundations, mostly consisting of alder wood, were shown to be in good overall condition generally. A comparison of normal and polarised light images of wooden cross-sections showed abundant crystalline cellulose within the cell walls, indicating that the state of conservation of the waterlogged samples is very close to that of sound alder wood. Only one alder sample showed signs of severe bacterial attack, mostly concentrated in the fibre cell walls. Radiocarbon dating identified two distinct construction periods. One sample dates to 1570 AD ± 85, whilst another dates to the year 960 AD ± 59. The later dating corresponds to the construction of the stone bridge that still exists today. The earlier period, around the year 1000, likely refers to the foundations of the first bridge, built after several pontoon bridges, and corresponding to the initial Ponte della Moneta.