The paper analyses the applicability of seismic base isolation made of elastomeric bearings for the seismic mitigation of architectural heritage buildings. Due to the inestimable cultural and historical significance any remedial measures into such objects must be selected with care and are usually very limited. In an ideal situation only interventions with minimum visual impacts on the object and maximum potential for restoring its cultural values would be implemented. Historical structures were usually not designed accounting seismic hazard and might be seismically more vulnerable as modern buildings. The paper deals with seismic base isolation as a technique for increasing the seismic resistance of architectural heritage buildings made of unreinforced masonry. Typical base isolation devices represent special bearings that are usually installed bellow the foundations of the structure. If the isolation system is properly designed it can eliminate the need for using more invasive retrofit measures and techniques. The paper presents a relatively simple and computationally less demanding technique for the modelling and analysis of regular unreinforced masonry (URM) structures. This technique is based on the equivalent frame approach, while the complex seismic failure mechanism of masonry piers is expressed by a single failure mode interaction surface (an "FMI surface"), taking into account the influence of variation in the pier's vertical loading, and it's bending moment distribution. A single failure mode interaction plastic hinge (an "FMI hinge") for each masonry frame element is introduced by combining specific failure modes, taking into account their minimum envelope. In the final part of the work a case study of using base isolation for the seismic retrofitting of an existing three-story masonry building has been conducted. Some results obtained by the N2 method comparing the damage in fixed based and base isolated variant of the test building demonstrate the potential of used techniques for the seismic protection of masonry heritage buildings.