The Development of the Mural Frontier in Britain from Hadrian to Caracalla* by David J. Breeze and Brian Dobson In 1936 in a short paper in the Journal of Roman Studies,1 Sir lan Richmond effectively demonstrated tha Antonine th t frontiery t 'ato e no t actuallWals bu ' wa l y embodied structural advances ove s Hadrianiit r c predecessor somd an , e year sRomans latehi n i r Britain gave h 2 e briea t concisbu f e accoun improvemente th f o t s introduce Antonine th y db e planners inte oth later Wall developmene Th . resula s ta experiencf to murae th f eo l barrier from Hadria Carao nt - calla has, however, never been examined in detail: the purpose of this paper is to study this development. Hadrian's Wall, from the start of building in the early 120s to its abandonment when the Antonine earl e Walbuils th ywa n l ti 140s, underwent several modifications. When first planned the units closesfrontiee th o t Romaf ro n Britain appea havo rt e been accommodate seriea n di s of forts base Agricola'n do s road from Carlisl Corbridgeo et Stanegatee th , lina ,f com o e - munication through one of the few convenient east-west gaps.3 The forts were at half the normal interval of one day's march, allowing the rapid assembly of a force to meet an attack on whatever scale or to go on the offensive, striking up from Corbridge or Carlisle. Beyond the road to the west Kirkbride - and possibly Drumburgh4-may have housed units to control the localpopulation guard an Solwaye d th ease newle th th t o t ;y discovered for t Whickhaa t havy mma e formed part of a system of protection of the south bank of the Tyne, unbridged below Corbridge. Between Stanegate fortcertaith e n th so f no e from Corbridg Carlislo et e fortlets have been discovered- Haltwhistle Burn and Throp as yet are the only two certainly known - and the system, such as it wascompletes wa , numbea y db lookouf o r t posts, most placed forwar line fortf th ed o f dso an fortlets. The fortlets may have housed units which were more concerned with control of movement, tha patrollins i t watchtower-mannind an g g duties functioe th , n later assume Wale d th an ly db milecastles it watchtowerd san s (turrets). This syste mf deploymeno f unitso t , however satisfactor r dealinyfo g with major attacks, could not deal with the problem of infiltration by raiding parties or cope with the whole business of contro movementf o l . Hadrian decide construco dt onle th t y for f effectivmo e controe th n i l absence of a natural barrier, an artificial barrier which could only be crossed at controlled points. This gave securit provinc e possibilite th th o yt d ean economif yo c developmene th t o right p u t frontier. This barrie originalls a r y planne consiso t s stona f dwa o t e wal Roma0 1 l n feet wide and perhaps 15 high to a parapet walk for the eastern 45 miles, and a turf wall 20 Roman feet wide at base and probably 14 high5 to parapet walk for the western 31 miles. In front of the Wall * This article is based on the paper read by the first author to the Society of Antiquaries of Scotland at their one-day conference, 'The Two Walls', 1st May 1971. I PROCEEDING 0 11 SOCIETYE TH F SO , 1969-70 1 :T~«—""tr- • i f u» • » J —L • • u • TJ-TT LJ• • LJ • • LJ • • U *^ r LJr • LJ L- ______'::::;' J------_-_ 1^3——I———————————' '.-INjji . .——"~~~T ~t:-;=.;-.:.-:;|.-J-~ ~ Li'lJ^~ ---/ - ——- -- UJ^- - —T — __._-- CD—————CD—————HC3——-——CJ d "FI 1 GHadrian' Antonine s th Wal d an l e Wal diagrammatin li c form . Hadrian'a . s Wal originalls la y plannet dbu not completed. Main features: wall and ditch with turrets, pierced by milecaste gateways; pre-existing forts behind the line . Hadrian'b . s Wall original pla modifies na d under Hadrian. Main features: walditcd an l h with turrets, pierce milecastly db e gateways; forts astrid walle eth , Vallum behind with crossing t fortsa s only . Antonin.c e Wall. •Main features: rampart with ditch; forts, with annexes, attache rampartdto ; fortlet beacon-platformsand s where -necessary; Military Way . Hadrian'd . s Wall from early third century. Main features: wall with ditch; some turrets; pierced by reduced milecastle gateways; forts; Military Way there was to be a ditch wherever necessary. This ditch varied in width from 26 to 34 feet, with emphasie th lowee th abous n r o sfigure wa fee9 td tan , deelittla r po e more t regulaA . r mile intervals along the Wall gates were to be placed, each guarded by a fortlet or milecastle BREEZ DOBSOND EAN MURAL E TH : FRONTIE BRITAIN RI N FROM HADRIA CARACALLO NT | A11 1 containing one or two small barrack-blocks, and each apparently provided with a lookout tower ove norte th r h gate.6 Between each milecastle therturreto tw e r lookoue werso b o et t towers, regularly spaced. Along the exposed west flank of the Wall, the Cumberland coast, milecastles d turretan s (for convenience distinguishe s milefortletda d towersan s ) wer ee built b als o ot , though no continuous wall was provided, the sea being considered a sufficient barrier. The line of frontier control was thus to extend from Newcastle-upon-Tyne, Hadrian's new bridge across the Tyne, for possibly nearly 120 miles to St Bee's Head. There is also some evidence that the south bank of the Tyne was defended, and certainly a new fort was built at South Shields, at the mouth of the river, though this may be a later addition. The troops to garrison the mile- 7 castle turretd an s s were probabl providee b auxiliare o yth t y db y units statione line f th eo n di forts already in existence on the Stanegate a mile or two behind the Wall; there is no evidence for a separate force. In the event of an impending invasion from north of the Wall, these units would be expected to move up through the milecastle gateways to fight the enemy in the field. purpose Wale Th th f l e Romao e itself th s a , n biographe Hadriaf o r divido t s e ne th wa tell , sus barbarians from the Romans. The military units had no special part to play in the control of movement unles militarsa y threat8 developed; they remaine thein do r natural lin communicaf eo - tion. The fortlets were presumably abandoned as the milecastles were occupied and the lookout towers were either incorporate systew d ne int r abandonedme o oth . In the course of putting this scheme into operation, when it was something over half- completed importann a , t chang frontiee mads th ewa o et r complex. decides wa t abando9I o d t n the forts immediately south of the Wall and replace them by new forts actually on the line of Walle th . This decisio clearls nt wa undertake yno n lightly t involvei r fo , t onl abandone dno yth - ment of permanent forts and the erection of new ones but also the demolition of milecastles, turret lengthd san Walf so l already constructe infilline th d ditche partf gdo an th f so . Thesw ene forts, placed about seven miles apart astridy la , Wale eth l whereve locae rth l topography allowed, with three twin-portal gates providin equivalene gth milecastlx si f o t e gates Walle nortth f h.o The purpose behind this change seems to have been to allow unrestricted access for major aree forceth a o Wale t norts th f l ho whic h would hitherto have been difficult with milecastle gate negotiateo st extremels i t I . y unlikely tha milecastle th t e gate kine s werth use dw r deno fo of sorties that have sometimes been envisaged,10 with the enemy rolled up against the Wall; this type of warfare was not in keeping with normal Roman practice. The new forts were only 1 part of the Wall complex for convenience; the conversion of a mobile1 field army into a frontier police force had not yet begun, though the temptation to make this conversion now existed. All the forts would seem to have been planned to project north of the Wall wherever possible. However, it was soon realised that, with the forts on the line of the Wall itself, so many gates opening north of the Wall were unnecessary. Hence at Halton Chesters both portals of the west gate were apparently blocked before the erection of the gateway was completed, and at Housesteads, with only one double gate opening north of the Wall, the east portal was built up at a similar stage.12 The fort of Greatchesters, one of the last of the primary series of forts completede b o t buils wa ,t wholly sout , thoughof h still attache Wale th , l dto althoug t coulhi d perfectly well have projected. The same is also true of Carrawburgh, added at a late stage in building to plug the long gap between Chesters and Housesteads. At Birdoswald too modifica- tions, probably lat Hadrian'n ei s reign, reduce numbee dth f portalo r s Wale nortth f lh o fro m six to two.