The Kingdom or Domain of Soissons is the historiographical name for the de facto independent Roman remnant of the Diocese of Gaul, which existed during late antiquity as a rump state of the Western Roman Empire until its conquest by the Franks in AD 486. Its capital was at Noviodunum, today the town of Soissons in France.
The rulers of the rump state, notably its final ruler Syagrius, were referred to as "kings of the Romans" (Latin: ) by the Germanic peoples surrounding Soissons, with the polity itself being identified as the , "Kingdom of the Romans", by the Gallo-Roman historian Gregory of Tours. Whether the title of king was used by Syagrius himself or was applied to him by the barbarians surrounding his realm (in a similar way to how they referred to their own leaders as kings) is unknown. However, it is most likely that they never referred to their leaders as kings because the Romans saw the word "king" or Rex in Latin as taboo because of its association with the tyrannical early Roman kings.
The emergence of a visibly autonomous Roman polity based around Noviodunum can be traced back to the appointment of Aegidius as of Roman Gaul by Emperor Majorian. When Majorian was killed on the orders of Ricimer in 461, Aegidius maintained his own power in the remnants of Roman Gaul against Franks to his east and Visigoths to his south.
Aegidius died in 464 or 465. His son Syagrius succeeded to the rule. In 486, Syagrius lost the Battle of Soissons to the Frankish king Clovis I and the domain was thereafter under the control of the Franks.
History
thumb|left|Domain of Syagrius (north-west) within the [[Western Roman Empire (blue)]]
The Kingdom of Soissons originated in the reign of the Western Emperor Majorian (457–461). Majorian appointed Aegidius to be magister militum of the Gallic provinces. The remaining Roman territory in Gaul in the north-west was connected with the Roman possessions in the Auvergne, Provence and Languedoc which connected these to Italy. During Majorian's reign, that corridor was annexed by the Germanic tribes now occupying Gaul, thus effectively cutting off Aegidius and his citizens from the Empire. Majorian and Aegidius had recovered the Roman position in most of Gaul, but with the death of Majorian in 461 the Roman position in the center and south deteriorated. These provinces were annexed by the Visigoths and Burgundians in the years 462–477, which left the remaining Roman territories in Gaul isolated.
Aegidius was allied with the Alans, and with Childeric I, king of the Salian Franks of Tournai and helped them defeat the Visigoths at Orléans in 463. According to Gregory of Tours, Aegidius even ruled the Franks during Childeric's banishment, but Childeric later returned from exile. It is possible that the Groans of the Britons, referring to a Romano-British request for military assistance after the Roman departure from Britain, may have been addressed to Aegidius.
Aegidius continued to govern until his death in 464. His comes, Paulus of Angers, was killed shortly afterwards, possibly on the same campaign. At that point Aegidius's son, Syagrius, took his place as ruler. Syagrius governed using the title of dux (a provincial military commander), but the neighboring Germanic tribes referred to him as "King of the Romans"; hence one of the nicknames of his enclave. Syagrius fled to the Visigothic king Alaric II, but the Franks threatened war if Syagrius were not surrendered to them. Syagrius was sent back to Clovis, who had him executed in 486 or 487.
[[File:Map Gaul divisions 481-fr.svg|left|thumb|The Kingdom of Soissons was a remnant of the Roman Empire within Gaul surrounded by newly established Germanic kingdoms.
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Clovis I ruled the Franks until his death in 511. When he died, the Frankish realm was divided into four kingdoms, one for each of his sons. Clothar I received a portion centred in Soissons, where he had been born a decade after Syagrius' death. Clothar survived all his brothers and their families—in one case by murdering the sons of a deceased brother—and eventually reunited the realm in 555.