The volume includes in this electronic version the abstracts and lectures given during the 13^th edition of the International Conference on Historic Structures held in Cluj-Napoca and Şimleu Silvaniei, having as topic Historic Load-bearing Structures in Ruins – Fortress Engineering. The lectures and the discussions were centred around the complex problem of the fortress engineering regarding the historic load bearing structures  from the point of view of specialists of different areas, including biology and building physics.