Argolis Cluster

The Argolis Cluster is an area of space containing a protostar cluster, as well as six star systems. One of these systems, the Tagra planetary system, was the location of the inhabited Tagra IV. This was the homeworld of the Tagrans. (TNG: "I Borg", "True Q") The cluster is located close to the Demilitarized Zone with the Cardassian Union and extends into three sectors of the Alpha Quadrant, including Sector 21505.

In 2368, the USS Enterprise-D conducted a survey of the Argolis Cluster's star systems as a possible prelude to Federation colonization. During the survey, it discovered a crashed Borg scout ship with one surviving drone, who would later be known as Hugh. A few months later in 2369, the Enterprise returned to the Argolis Cluster to provide ecological assistance to Tagra IV. (TNG: "I Borg", "True Q") An attempt to establish a colony in the cluster in 2381 ended in failure.

During the Dominion War, the Dominion concealed a large sensor array at the periphery of the Argolis Cluster. The array allowed them to monitor allied ship movements over five sectors, providing them with a substantial tactical advantage. In 2374, the USS Defiant, successfully destroyed the array by moving through the cluster instead of around it. The Dominion forces were unprepared for an attack from that direction, as they believed any ship inside the cluster would be destroyed by the extreme gravimetric shear. (DS9: "Behind the Lines")

Later in 2374, the Dominion attempted to establish a supply line to the Argolis Cluster through Betazoid space, which would have allowed them to attack Vulcan. (DS9: "The Reckoning")