The Roman Army, 31 BC–AD 337: A Sourcebook

The army in the field 109
encouraging the sick, and providing an example for everyone. But the
severity of the climate and service conditions caused many to refuse
their duties or desert. Corbulo sought the answer in toughness. For he
did not, like other commanders, extend a pardon to first and second
offenders, but immediately executed anyone who deserted the standards.
Experience showed that this was beneficial and more effective than
leniency, since Corbulo had fewer deserters from his army than those
commanders who were indulgent.
Cf. Fronto Principia Historiae 12=Loeb, vol. 2, p. 208. The legions stationed
in the east seem to have had a particularly bad reputation for ill-discipline.
That is perhaps because in Syria the soldiers were quartered in towns, not
camps, and were consequently more difficult to control. But it may simply be
that we have more evidence for Syria than for other provinces because of the
eastern campaigns of Corbulo and Lucius Verus, reported by Tacitus and
Fronto, who may indeed have exaggerated the extent of earlier indiscipline in
the Syrian army.