His share was based in the centre of the Frankish Kingdom, with his capital at Soissons, and consisted of the Parisian basin, the Massif Central, the Languedoc, Provence, Burgundy, southern Austrasia, Alsace, and Alemannia; the regions were poorly integrated and surrounded by those bequeathed to Charlemagne, and, although Carloman's territories were easier to defend than those of Charlemagne, they were also poorer in income.

The brothers shared possession of Aquitaine, which broke into rebellion upon the death of Pepin the Short; when Charlemagne campaigned to put down the revolt, Carloman led his own army to assist.

[7] Rosamond McKitterick has argued, however, that our assumption about the relationship between the two brothers can't be based solely on a few examples and that there is no evidence to suggest that there was lasting animosity between the two.

She also points out that Charlemagne showed great political pragmatism and astuteness throughout his reign and that it would have been in the brothers' common interest to work together to secure their dynasty's control over the Franks, having only recently gained royal power.

[10] Carloman died on 4 December 771 at the Villa of Samoussy; the death, sudden and convenient though it was, was set down to natural causes (a severe nosebleed is sometimes claimed as being at fault).

Carloman married a Frankish woman, Gerberga, who, according to Pope Stephen III, was chosen for him, together with Charlemagne's concubine, Himiltrude, by Pepin the Short.

Desiderius and his family were captured, tonsured, and sent to Frankish religious houses; the fate of Gerberga and her children by Carloman is unknown, although it is possible that they, too, were sent by Charlemagne to monasteries and convents.