The Symposium on The Acoustics of Ancient Theatres, the second on this topic after the one held in Patras (Greece) in 2011, aims to bring together experts to present and discuss all aspects related to the acoustic properties of these monuments which are often still used for public performances including opera, drama, speech and music. The evolution and development of new technologies for the multichannel measurement systems, together with acoustic simulations, auralisation methods and virtual reconstructions, have generated renewed interest in these spaces. These aspects, as well as more interdisciplinary studies, will be presented and discussed. The event will be included among the initiatives of the International Year of Sound (IYS 2020) promoted by the International Commission for Acoustics (ICA).