As Earth gained it first major victory at Berengaria and began amassing forces for the retaking of Deneva, Romulan supreme commander Valdore withdrew forces from Deneva in preparation for the invasion of Tau Ceti IV. As Coalition forces attacked Deneva, the Romulan forces moved to attack the lightened defenses at Tau Ceti IV.
The Romulan fleet entered the system on June 20, 2156 and using its superior numbers, quickly overpowered the Coalition task force guarding it. Due to recent upgrades provided by the Cochrane Institute of Alpha Centauri, the Romulans were unable to hijack any vessels with their Arrenhe'hwiua remote control technology, so they turned to full force of their weapons on the Coalition ships. Andorian and Tellarite forces suffered heavy losses and retreated to the edge of the system, while most of the Starfleet ship were destroyed, including the Atlantis (NX-05). Following this, the Romulan fleet began heavy bombardment of the capital city, Amber, and landing troops on the surface.
The Romulans thus established a foothold within close range of Earth, only 12 light-years away. This led United Earth leaders to establish a "Fortress Earth" policy, in which a large number of Starfleet vessels were withdrawn from outlying regions to guard Earth and Alpha Centauri. (ENT - The Romulan War novel: Beneath the Raptor's Wing)