The Domain of Soissons, also known as the Domain of Aegidius and the Domain of Syagrius, is a rump state of the Western Roman Empire in northern Gaul (present day France) for some 25 years during Late Antiquity.The Domain of Soissons' evolution begins when Emperor Majorian (457–461) appoints Aegidius as magister militum of the Roman Gaul.

When Majorian loses his authority and his life to Ricimer in 461, Aegidius maintains his own rule in much of his province, creating a Roman rump state that comes to be known as the Domain of Soissons.

In the chaos of contemporary Gaul, he maintains his power against Franks to his east and Visigoths to his south; his relations to the Romano-British of Brittany may have been friendly.

Aegidius dies in 464 or 465.

His son Syagrius succeeds to the rule.

In 486, Syagrius loses the Battle of Soissons to the Frankish king Clovis I and the domain is thereafter under the control of the Franks.