Dux Britanniarum Dux Britanniarum was a military post in Roman Britain , probably created by Diocletian or Constantine I during the late third or early fourth century . The " Dux " ( literally , " ( military ) leader " ) was a senior officer in the late Roman army of the West in Britain . It is listed in the Notitia Dignitatum as being one of the three commands in Britain , along with the The Dux Britanniarum was commander of the troops of the Northern Region , primarily along Hadrian ' s Wall . At the imperial court the Dux had the highest ranking class of " viri spectabiles " . His responsibilities covered the area along Hadrian ' s Wall , including the surrounding areas to the river Humber in the southeast of the city of Deva ( Chester ) and today ' s Yorkshire , Cumbria and Northumberland to the mountains of the Southern Pennines . The headquarters were in the city of Eboracum ( York ) . The purpose of this buffer zone was to preserve especially the economically important and prosperous southeast of the island from attacks by the Picts ( tribes of what are now the Scottish lowlands ) and against Scots ( Irish raiders ) . History . The troubled north of the island was dominated by the military . The soldiers of the " Dux " were probably recruited almost exclusively in Britain . The " Notitia Dignitatum " lists the garrison along Hadrian ' s Wall ( along with several sites on the coast of Cumbria ) for a total of 38 units under the command of the Dux Britanniarum . Archaeological evidence shows that other units must have been stationed here , which are not , however , mentioned in the " Notita " . Most of them were established during the 3rd Century . ( Long time was that these troops list because of the relatively large number of High Imperial unit designations for antiquated , only more so keep ) in " Notita Dignitatum " because Britain was never officially abandoned by the Romans . Castles and units . His troops were " limitanei " or frontier guards and not the " comitatenses " or field army commanded by the Comes Britanniarum . Fourteen units in north Britain are listed in the " Notitia " as being under his command , stationed in either modern Yorkshire , Cumbria or Northumberland . Archaeological evidence indicates there were other posts occupied at the time which are not listed . His forces included three cavalry " vexillatio nes " with the rest being infantry . They were newly - raised units rather than being third century creations . In addition to these fort garrisons , the " dux " commanded the troops at Hadrian ' s Wall : the " Notitia " lists their stations from east to west , as well as additional forts on the Cumbrian coast . These troops appear to have been third century regiments , although the reliability of the " Notitia " makes it difficult to infer any solid information from it . From Chapter XL : . . . in addition to the administrative staff ( " Officium " ) lists 14 prefects and their units with their deployment locations under the command of this Dux : Then follow the garrisons along Hadrian ' s Wall ( " per item lineam Valli " ) : and an unknown unit in the fort " Luguvalium " Origin . All these units are " limitanei " . ( However , it seems that some have stood for the " Comes Britanniarum " available . ) The ultimate list of the " Dux Britanniarum " was completed well ahead of the " Comes Britanniarum " . One should , however , ( not take the original edition of " Notita Dignitatum " literally ? ) , as this would place one unit ( " Segontienses " ) at Segontium ( Carnarvon in Wales ) . Since it is unlikely that field army units were used to reinforce remote garrisons , it appears the British " limitanei " were further reduced in order to fill them with the Gallic field army as " Pseudocomitatenses " . The " Cuneus Sarmatarum " was a cavalry unit recruited from Sarmatian horsemen . The " Equites Crispianorum " may have been named for Crispus , eldest son of Constantine I , who was executed in 326 AD for an alleged conspiracy , by personal order of the emperor . The continued existence of his name in this unit ( along with the " Auxilium Crispitienses " under the " Dux Daciae " ) shows that he probably did not fall within the otherwise rigorously handled " damnatio memoriae " ( i . e . , removing all mention of the condemned ' s existence ) . The men under the " Praefectus Defensorum Numeri " seem to be the same as the " Defensores seniores " ( " pseudocomitatensis " from Gaul under the command of " Master Equitum " ) . The men under the " Praefectus Numbers exploratorum " were reconnaissance and also a unit of Gallic " Pseudocomitatenses " ( with a " Master Equitum " as commander ) , but also partly the stand " Comes Litoris Saxonici " available ( stood available to the Commander of the Saxon Shore ? ) The " Legio sexta " is an ancient tribal legion of Britain , the " Legio VI Eburacum " ( York ) . Interestingly , they seem to have had in late antiquity no fixed posting . One might expect that this legion ( full name : " Legio VI Victrix Pia Fidelis Britannica " ) at this time still to be stationed in Eburacum : this absence may indicate that the unit had been moved to another site when the list of the " Dux Britanniarum " was compiled in the " Notita Dignitatum " . ( " Possibly is the VI . " ? ) but also in connection with the non - historically tangible " primani iuniores " in the army of the " Comes Britanniarum " . The men under the " Praefectus Numbers Solensium " could ( per Arnold Hughes Martin Jones , 1986 ) be the descendents of another British unit , the " Legio XX Valeria Victrix " . This is the only legion no longer listed in the " Notita Dignitatum " . The last epigraphic evidence of their presence in Britain is a mention on coins of the usurper Carausius , a century before the " Notita Dignitatum " was compiled .