Bauska fortress-ruin is a monument of architecture and archaeology of national significance. Bauska fortress was built in the middle of the 15th century under the rule of the Livonian Order as a massive protective building for firearms and a residence at the same time. In the last quarter of the 16th century the castle was rebuilt into a fortified residence of the Dukes of Courland. In 1706, during the Great Northern war, the fortification systems of the castle were blown up. After the war the building has lost its functional significance; it has not been repaired and has gradually turned into romantic ruin. Before conservation Bauska fortress-ruin was in a condition of breakdown, which was rapidly progressing, and the existence of authentic evidence of 15-16th century building history was threatened. For three centuries the roofless walls of the castle have been exposed to precipitations and accelerated erosion. Deep caverns and cracks have appeared. Mortar and masonry wedging have been washed out of the joints, static defects have appeared. The unstable masonry constructions caused threat to visitors of ruins and hindered the use of the site for active cultural and educational work: excursions, concerts, performances and festivals. The first stage of Bauska fortress-ruins conservation within the framework of program ls"Culture 2000' by the European Commission has been completed covering the most endangered part of the ruins with the area of 890m2. An international symposium was organized in the initial stage of the project in which specialists discussed different methods of the historical building ruin preservation analyzing experience from the Mediterranean basin, Central Europe, the Baltic and Scandinavia. The conservation conception of Bauska fortress-ruins and technical projects, developed by renovation atelier of historical buildings ls"Girsa A.T.' (Czech Republic) was presented during the symposium. The practical conservation works were completed by the restorers of Czech company ls"Miloscaron; Gavenda' in a joint team with the employees of the Bauska Castle Museum. Conservation was carried out in 2002 within the scope of programme ls"Culture 2000' and was continued in 2003. In spite of the fact that the technical condition of the ruins was on the point when their saving could be impossible, in the part of ruins subject to conservation the process of destruction was stopped and the static stability of masonry was achieved by minimum interference with the substance of the site; maintaining the story-telling value of the masonry, visual signs and aging patina fully complies with the project concept: to fully preserve the original construction, at the same time not losing the romantic air of the ruins and their historical and emotional value. In the course of works the ruins of the ancient building were made more comprehensible by highlighting the historical information comprised by the walls, or by making it more precise. The fragments of the building bearing information on the decorations of premises, positions of corners, apertures, coverings, and reconstruction were fixed with utmost care. Bauska project offers a specific philosophical and both technically and technologically elaborated approach to preservation of torsel architecture, which has been tested in practice. The quality of conservation works was ensured by study of the historical crafts and materials, and their application. The historical building is an inexhaustible source of knowledge: the works included the selection and preparation of materials, treatment of stones, selecting techniques for laying bricks and stones, as well as treatment of surfaces and formation of textures. The process of performing conservation works was organised as a site for international discussions of experts and a place for training renovators and workers freely accessible to wider public. Project implementation clearly demonstrated the advantages of cooperation by experts of various European regions in maintaining cultural heritage because a possibility was created to solve problem situations in the presence of international experts. The conservation project was evaluated on international level by a symposium organised by Bauska Castle Museum "Renaissance of the historical crafts and synthesis of modern technologies in the maintenance of medieval masonry"; its implementation was analysed in an international conference "Experience of implementation of the first phase of the 15th century Bauska fortress-ruin conservation"; materials of the symposium and conference are published by Bauska Castle Museum in the edition "The Problems of Historical Ruin Conservation", 2002, and Zpravy pamatkove peče, Praha, 63/2003, No.4. The training of renovators that was started in the course of the project is continued annually. The project addressed a number of social problems. Several unemployed individuals registered by the Latvian State Employment Service were engaged as auxiliary workers in the conservation works. They participated also in the theoretical training, which can be considered a process facilitating rehabilitation of these individuals. Project implementation was awarded with Annual Award of the State Inspection for Heritage Protection in renovation in 2002 and in 2004 with EU prize for Cultural Heritage - Europa Nostra Diploma for Architectural Heritage.