St. Mark's Church is one of the most recognisable sacred historical buildings in Zagreb. Built in medieval times, the church has been a witness to many historical, liturgical and stylistic changes. In the 17th and the 18th century the church was home to one of the richest baroque interiors in continental Croatia. There were thirteen altars with more than hundred sculptures altogether, each of the altars representing one of the city’s numerous guilds. However, to a contemporary eye the baroque layer is invisible today. With the arrival of the 19th century and the purification fashion in art history, much of the earlier inventory was forever lost or found its new home in museums. The aim of this thesis is to present the complete catalogue of all the altars in the middle of the 18th century and to offer a virtual restitution of the interior. In order to do that the researcher analysed the available literature concerned with the baroque period in the church and did the archival research. In the first part of the thesis the researcher gives a critical review of the literature. In the second part of the research there is a short historical overview of the pre-baroque period and the post-baroque period as well as the elaborated analysis of the baroque renovation, iconography and all the preserved baroque sculptures. An important discovery during research was a complete photo documentation of the preserved sculptures in the photo-archive of the Institute of Art History which has helped to offer a better insight into the inventory. The most important parts of the thesis are the virtual restitution, which was done according to canonical visitations in Photoshop, and the complete catalogue of all the altars from the church. The catalogue provides an overview of all thirteen altars and the pulpit regarding the sculptures, iconography, the guilds and the donors. It acknowledges that today there are in fact two preserved altars from the church, whereas in the previous literature only one was assumed to be preserved.