Many Franks were already serving in the Roman Army. Others were raiding Eastern Gaul. The Emperor Julian allowed the Salian Franks to settle with the Batavian Foederati between the Maas, Waal and the Rhine west of Nijmegen.
Germanic Peoples are shown in Green The Gewissae on the upper Thames are a band of ex- Roman Army Germanic Soldiers. Click on the map to enlarge.
The Domain de Soissons was regarded as part of Lugdunensis (see Map B) by its Roman rulers. This area became the the last vestige of the Western Roman Empire. It was extinguished at the battle of Soissons in 486 where Syagrius was defeated by the Salian Frankish King Clovis of Tournai
Showing the expansion of the Frankish Empire started in 486 after the Battle of Soissons. I have shown the "Counties" of Haspengau, Rheingau, Wormsgau, Thurgau and Fezensac and the city of Thouars that were ruled by our direct ancestors also the "Dukedom" of Moselle and the County of Upper Alsace that were ruled by early members of our female line via Emma de St Martin de Varenne mother of the 1st Earl de Warrenne and her progenitors the De Courcy and Carolingian families.
shown the Gatinais ------ and the County of Anjou where our direct male ancestors were Counts if we assume the Plantagenet Line. The male Plantagenet Line descends from the Merovingian Kings then the Counts of Haspengau with Upper Rhine and Wormsgau, then the Counts of Thurgau, the Counts of Fezensac, Viscounts of Orleans, the Counts of Gatinais then the Later Counts of Anjou after Geoffrey II Ferreol, Count of Gatinais (lived ~ 1000 to 1046) married the heiress Ermenegarde of Anjou daughter of Fulk III Count of Anjou; a descendant of Sigimerus and Charlemagne (see note on Map D above).
Lugdunensis II, the Eastern part of Lugdunensis III and Lugdunensis Senonia were the basis of the realm of the Roman Dux Syagrius, the last vestige of the Western Roman Empire in Gaul. This realm is called the Domain de Soissons in some French Histories. See Map C below.
Herfast III, (son of Herfast II, Forester of Arques), was probably awarded the manor of Crepon by his sister Gunnora's husband Richard I, 3rd Count of Normandy.
Dalmatia and some parts of Galliae and Septem Provinciae (see Map B) had remained under the Western Emperor Nepos ( the Nephew of the Eastern Emperor Zeno) even after Italia had been seized by Orestes, (the Magister Militum) who put his son Romulus Augustulus on the throne of the Italia remnant of the Western Empire. Romulus was deposed by Odoacer the Goth in 475 but Nepos survived until he was murdered by his soldiers in 480, when Odoacer conquered Dalmatia. The other Dioecesis of the Western Roman Empire were conquered by the Suevi & Visigoths in Hispania, the Moors, Vandals and Alans in Africa & the Salian Franks, Burgundians, Alamans and various other Teutonic Tribes in Gallia and the Salian Franks, Visigoths and Burgundians in Septem Provinciae.
In 418 Honorius gave the Visigoths settlements as foederati (under the Roman practice of "hospitalitas") in Aquitanica I & II.
Roman "Rule" in South Western and Southern Gaul (a good reference for these times is here ) started to disintegrate in 462 when the remnant government of the Western Roman Empire, controlled by Ricimer in the name of Libius Severus, granted the Visigoths Aquitanica I & II, Novem Populana and Narbonensis I to settle. In 469 the Visigoths invaded Provence (Narbonensis II, Southern Viennensis and parts of Alpes Maritimus)and defeated a combined Army of Romans, Soissonians, Burgundians and Britons. In 475 the Visigothic king, Euric, ceded Provence to the Empire by a treaty whereby the Eastern Emperor Julius Nepos recognised the Visigoths' full independence.
By 477, the Visigoths had conquered all of Provence and most of Hispania. However they lost most of their Gallic lands to the Franks by 531, although they held on to Septimania (most of Narbonensis I) until 759.
Roman "Rule" in Greater Burgundy effectively ended in 476 with Odoacer's takeover of Italia and the Burgundians and Alemans gaining rule over Lugdunensis I, Septem Provinciae east of the Loire (except for Septimania, the coastal strip), Maxima Sequanorum and the northern Alps. The Burgundians ruled Burgundy (Map D) until 536 when they were conquered by the Franks.
Syagrius (Dux under Emperor Nepos) ruled what he called Belgica Secunda, but actually per Maps B & C all of Lugdunensis except Lugdunensis I and Armorica (Brittany) until defeated by Clovis I King of the Salian Franks, who ruled Austrasia, at Soissons in 486, see Map D below. This started the expansion that created the Frankish Empire. Julius Nepos was murdered in 480, nevertheless Syagrius carried on issuing coinage in his name until Syagrius was defeated by Clovis I in 486. Thus Roman "rule" in Gaul was virtually extinct by 486.