This thesis explores Salona, the capital of the Roman province of Dalmatia, with a particular focus on the period of Emperor Justinian I's reign during the 6th centuries. The research emphasizes architectural and archaeological aspects, especially the fortification system built and restored to protect the city from frequent invasions and internal conflicts. Justinian's construction activities, including the building of churches and defensive structures, significantly contributed to the military and religious importance of Salona in late antiquity. The period of Emperor Justinian I's rule was the last great era of progress for Salona, which, despite all efforts, could not avoid its destined decline in the 7th century, leading to the gradual abandonment of the city. Through a combination of historical analysis and archaeological evidence, the thesis provides insight into the complex processes that shaped the rise and fall of Salona, thus contributing to the understanding of the broader context of late antique urban development.