There  were  no  doubt  reasons  of  policy  which  led  him  to  make
hia  Dacian  and  Oriental  expeditions,  but  nevertheless  they
were  mistakes.  The  time  for  conquest  was  gone  by ;  and  the
truest  wisdom  would  have  been  to  have  rested  content  with
the  limits  which  had  been  fixed  by  Augustus — the  Rhine,  the
Danube,  and  the  Euphrates.  Trajan's  conquests  had  for  the
most  part  to  be  surrendered  immediately  after  his  decease ;  and
the  prestige  of  Rome  was  more  injured  by  their  abandonment
than  it  had  been  advanced  by  his  long  series  of  victories.
Trajan,  on  his  return  from  the  East,  found  his  health  failing.
He  was  sixty-five  years  old,  and  had  overtaxed  his  constitu-
tion by  the  fatigue  and  exposure  which  he  had  undergone  in  his
recent  campaigns.  He  had  nominated  no  successor  before
quitting  Rome,  and  it  was  now  of  the  last  importance  to  supply
this  omission.  But  regard  for  the  constitutional  rights,  which
it  had  been  his  policy  to  recognize  in  the  Senate,  induced  him
to  postpone  the  formal  act  as  long  as  possible,  and  it  is  uncer-
tain whether  he  did  not  delay  till  too  late.  The  alleged  adop-
tion of  Hadrian  by  his  predecessor  was  perh^s  a  contrivance
of  the  Empress,  Plotina,  after  the  death  of  her  husband.  It
was,  at  any  rate,  secret  and  informal ;  and  the  new  throne  was
consequently  unstable.  But  the  judicious  conduct  of  Hadrian
in  the  crisis  overcame  all  difficulties ;  and  his  authority  was  ac-
knowledged without  hesitation  both  by  the  army  and  the  Sen-
ate.
Hadrian,  who  succeeded  Trajan  in  A.D.  117,  had  a  reign  of
nearly  twenty-one  years  (from  August,  A.D.  117,  to  July,  A-D.
