Zadar, situated on the eastern Adriatic coast, reflects over two millennia of uninterrupted human activity. The city's rich history has yielded an equally valuable cultural heritage, with its cultural legacy serving as a topographical testament to the traditions and artistry of Dalmatian inhabitants since ancient times. This thesis narrows its scope to the periods of Zadar's antiquity and the Middle Ages. Despite being distinct historical and stylistic eras, their identities within the city's walls are intricately intertwined. The main concepts of the thesis centre around the synergy and integration of one era into the temporal framework of another on an architectural level. The described interaction between antiquity and the Middle Ages was approached through the prism of the architectural phenomenon of the use of spolia. The primary objective of the thesis was to compile a comprehensive and systematic inventory of ancient spolia in medieval structures. The survey of ancient spolia in Zadar's medieval heritage considers both sacred and secular architecture. Churches from the early, mature, and late Middle Ages are examined, where elements from antiquity were incorporated into their structures.