The ancient bridge, and above all that connecting the two banks of a river, is often a difficult object to survey precisely for the specificity of the external environmental factors touched on above. The case studies examined in the Lusitania region – the bridges of Alconetar, Alcantara, Segura and Vila Formosa – represent unique instances for their current state of conservation and especially for the topographic and orographic complexity of their position, which makes the planning of the three-dimensional survey extremely complicated.