This paper proposes a Portuguese backbone network of reference consisting of the network physical topology and traffic matrix. The physical topology is obtained by first taking into consideration the backbone links that are already in use by telecommunication operators in Portugal and then superposing them to build a unique infrastructure intended to support all the backbone traffic in Portugal. Based on available statistical information concerning the voice and data traffic demands in Portugal, a traffic matrix with the average traffic demand between each node pair of the backbone network is devised. The proposed physical topology and traffic matrix can be seen as a first step towards defining a Portuguese backbone network of reference that can be used in academic and scientific studies, in particular for those regarding optical communications, optical networking and traffic engineering.