Whilst  the  Jewish  rebellion  was  taxing  the  militar)


lOO  THE    YEAR   OF  FOUR   EMPERORS

resources  of  Rome  in  the  East,  a  grave  danger
threatened  the  Rhine  frontier  and  North-Eastern
Gaul.  The  Roman  army,  it  will  be  remembered,
consisted  in  large  part  of  "  auxiliary "  troops  levied
from  the  subject  peoples,  who  were  thus  gradually
absorbed  into  the  ruling  race.  It  was  a  bold  and
liberal  policy,  which  had  hitherto  proved  successful,
since  the  loyalty  of  the  auxiliaries  had  been  un-
questioned. Nevertheless,  it  is  easy  to  see  that  there
was  danger  of  friction  between  these  troops  and  the
legions,  who  enjoyed  the  privileges  of  Roman  citizen-
ship, and  this  was  the  more  likely  to  arise  in  the
case  of  corps  which  were  officered  not  by  Romans,
but  by  leaders  of  their  own  nationality.  Amongst
these  were  the  cohorts  of  Batavians,  whose  home  was
in  the  delta  of  the  Rhine.  The  Batavians  paid  no
tribute  to  Rome,  but  were  subject  to  the  "  blood-tax,"
which  drew  the  flower  of  their  youth  to  serve  in
the  Roman  cavalry.  Eight  of  these  regiments,  which
had  won  distinction  in  the  conquest  of  Britain,  had
been  recalled  by  Nero  at  the  close  of  his  reign,  and
had  become  disaffected  because  two  of  their  leaders
were  falsely  accused  of  treason.  They  quarrelled
with  the  soldiers  of  the  Fourteenth  Legion,  with
which  they  were  brigaded,  fought  against  the  legion
at  Betriacum,  and  when  ordered  to  accompany  it
back  to  Britain,  refused  to  obey  and  marched  to
Moguntiacum  (Mainz).
