This paper presents the retrofit project of a 150 year-old cathedral that was severely damaged after the March 3rd, 1985 central Chile earthquake, and the February 27th, 2010 Maule earthquake. The project is being developed by a team of architects and structural engineers from two Chilean companies, the latter dedicated to structural engineering and seismic protection of structures. The Basílica del Salvador is located in Santiago and was built towards the end of the 19th century. The unreinforced brick structure is approximately 90m long, 40m wide, 25m high and has suffered extensive damage during major Chilean earthquakes over the past century. Currently, several areas of the structure are partially collapsed and many architectural components are damaged, making the retrofit project very unique and challenging. The overall concept of the retrofit is to recover the original architecture and aesthetics of the church while improving its seismic safety standard to optimal conditions, by introducing seismic isolation between the superstructure and a new underground level. The retrofit project considers two stages:(i) a temporary stabilization phase, which involves adding a steel shoring structure inside the main auditorium to support the partially collapsed columns and unstable exterior walls, and (ii) a permanent phase, which involves the addition of a new underground level, the introduction of seismic isolation to protect the superstructure and the architectural restoration of the superstructure.