The Sim
In the 2380's, the cube encountered two Tal Shiar vessels. While one ship was spared, the second, the Shaenor was assimilated. Shortly after assimilating the Romulan ship, a submatrix collapse was triggered on the cube which immediately severed its link to the collective.
Shortly thereafter, the cube was claimed by the Romulan Free State who declared the cube the Borg Artifact Research Institute or The Artifact and established a base, The Romulan Reclamation Site,within the cube to facilitate research.