The Roman Amphitheater in Cagliari is a significant witness to Roman culture in Sardinia and one of the most celebrated monuments of the Sardinian capital. Dated between the first and second centuries CE, the amphitheater has been referenced by several classical sources; however, from the eighth century, information about it becomes scarce and fragmentary. During these centuries, the monument gradually lost its importance and was frequently repurposed as a quarry for building materials. Starting in the nineteenth century, the ruins of the amphitheater became the subject of study by various European scholars traveling to the island, as well as by local researchers. This renewed interest led to a gradual rediscovery of the site, not only by the academic community but also by local authorities, the municipality, and citizens. However, throughout the nineteenth and twentieth centuries, interventions related to protection, archaeological excavation, and conservation were often fragmented. The ruins were subjected to interventions and uses that were not always appropriate for their archaeological and structural characteristics. For example, in the early decades of the twentieth century, the site was illegally inhabited by criminals, and in the post-war period, it was occupied by displaced people. From the late 1950s, the amphitheater was used during summer seasons for theatrical performances, concerts, and other events, with temporary structures being added that eventually became permanent. Recently, these structures have been removed, and the amphitheater is currently neither accessible nor usable. It now awaits a new approach to conservation, enhancement, and adaptive reuse that respects its archaeological significance. Building on these brief historical considerations, the aim of this paper is to analyze and reflect on the conservation actions and practices implemented on the monument from the late nineteenth century. This analysis is based on an investigation of diverse historical sources—including archival, bibliographical, iconographic, and cartographic materials—to reconstruct the long history of the site, marked by various uses, abuses, protection interventions, and enhancement initiatives from antiquity to modern times.