It was formed as a result of Emperor Basil II’s annexation of a portion of the Bagrationi dynasty domains (1000–1021) and later aggrandized at the expense of several Armenian kingdoms acquired by the Byzantines in a piecemeal fashion in the course of the 11th century.

These areas – parts of the Armeno-Georgian marchlands centered on Thither Tao, including Theodosioupolis (now Erzurum, Turkey), Phasiane, Hark’, Apahunik’, Mardali (Mardaghi), Khaldoyarich, and Ch’ormayari – had been granted to David for his crucial assistance to Basil against the rebel commander Bardas Sclerus in 979.

This changed, however, when Constantine IX Monomachos (1042–1055) dismantled the army of the theme of Iberia, perhaps 5,000 men, converting its obligations from military service to the payment of tax.

Constantine's reforms caused great discontent in the theme and exposed it to hostile attack aided by the removal of regular troops from the region, first to crush the Macedonian revolt of Leo Tornicius, himself the former catapan of Iberia (1047),[8] and later to halt the Pecheneg advance.

In 1051/52, Eustathius Boilas, a Byzantine magnate who moved from Cappadocia to the theme of Iberia, found the land "foul and unmanageable... inhabited by snakes, scorpions, and wild beasts.

"[6] About 1053 Constantine IX disbanded what the historian John Skylitzes calls the "Iberian Army", which consisted of 50,000 men, and was turned into a contemporary Drungary of the Watch.

Two other knowledgeable contemporaries, the former officials Michael Attaleiates and Kekaumenos, agree with Skylitzes that by demobilizing these soldiers Constantine did catastrophic harm to the Empire's eastern defenses.

Still, it may have lasted as late as 1074 when Gregory Pakourianos, a Byzantine governor, formally ceded a portion of the theme including Tao and Kars to King George II of Georgia.