Rome, the Greek World, and the East, Vol. 2 - Government, Society, and Culture in the Roman Empire

Emperors, Frontiers, and Foreign Relations 179

bythenewPersiandynastyoftheSassanidswasoneofthoseconsequences,
Herodian’saccount(6,2–3)ofRomanreactionsinthe220sand230sshows
veryclearlyhowrigidweretheassumptionswhichnowprevailedastothe
need for the imperial presence on all majorcampaigns. Letters came from
the governors of Syria and Mesopotamia to say that Artaxerxes (Ardashir)
wasthreateningthewholeeasternempire.SeverusAlexanderconsultedwith
hisamiciand sent an embassy with a letter warning Artaxerxes off; when
thiswasineffective,andthegovernorsoftheeasternprovinces‘‘werecalling
forhim,’’AlexandermarchedviatheDanubianprovincestoAntioch.After
furtherdiplomaticexchanges,hemountedatripleinvasionofArmeniaand
Mesopotamia.HewasbackinAntioch,probablyoverthewinterof232/3,
whenmessengersbroughtnewsofGermaninvasionsacrosstheRhineand
Danube,whichdemandedthepresenceofAlexanderandthetroopswhich
he had taken east with him.The force of these reports was intensified by
thereactionsofthosesoldierswhohadbeentransferredfromtheDanubian
provinces.Herodiancontinues:^87

Alexanderandtheadviserswhoaccompaniedhimwerebythistime

evenconcernedaboutItaly,ratingtheGermanmenaceasverydifferent

fromthePersians.Theinhabitantsoftheeasternterritories,separated

astheyarebyawidestretchoflandandsea,hardlyhearaboutItaly.But

theIllyrianprovincesareanarrowstretchoflandthatdonotoccupy

much of Roman territory.This makes the Germans practicallyadja-

centneighboursoftheItalians.Reluctantlyandsadly(throughsheer

necessity)Alexanderissuedtheproclamationofanexpedition.

HowevervagueandconfusedHerodianmaybe,itisafactthatinthissitua-
tionAlexanderfelthimselfcompelledtoundertakeamarchofmorethan
2,000miles,whichcannothavetakenlessthanaboutfivemonths.By234he
wasontheRhinefrontier,wherehewasmurderedatMoguntiacumin235.
Hehadruledassoleemperor;butonedirectconsequenceoftheassumption
thatemperorswouldconductmajorcampaignsinpersonwasthemultipli-
cationofemperors.Thisisalreadyclear,forinstance,in260:whenValerian
wascapturedbyShapurIinMesopotamia,hissonGallienus,asjointAugus-
tus,was conducting campaigns in northern Italy, and his grandson Saloni-
nus, with the title of ‘‘Caesar,’’ was commanding the Rhine frontier from
Cologne.PreciselysuchnecessitiesledtotheformationoftheTetrarchyand
thentothesuccessivesemi-dynasticcombinationsofemperorswhichchar-
acterizedthefourthcentury.AccordingtoZosimus,forinstance,itwasthe

87.6,7,4–5.