Stone masonry walls of natural limestone blocks and lime based mortar similar to those used in ancient structures are tested under vertical loading and presented in this paper. The research program includes testing of wall components as well as wall assemblages under vertical loads to study the different factors affecting the wall strength, ductility and load-deformation behaviour up to failure. The considered factors cover: natural limestone block strength, lime based mortar strength, the relative dimensions and composition of the wall assembly as well as the thickness of mortar joints. Two types of natural stones of different strength, several mixes of lime based mortar with different strengths, and different systems and composition of wall models are tested in this research. Twelve wall specimens are considered including six single leaf walls, five double leaf walls and one cavity wall with shear key. It was found that the type and strength of mortar has significant effect on the overall wall behaviour. Also of paramount importance is the effect of the thickness of mortar joints on the wall ductility. The stress distribution within the wall component was recorded during wall testing to failure for further analysis.