praemisso equitatu et essedariis
with the calvary and the charioteers having been sent forth
consuerunt
they were accustomed
egress prohibebant
they were preventing (them) from disembarking
propter magnitudinem
on account of their size
constitui
to be stationed/anchored
ignotis locis
in unknown places
gravi onere
with heavy burdens
oppressis
having been weighed down
desiliendum
had to be jumped down from
consistendum
it had to be stopped
progressi
having progressed
notissimis
very well known
audacter
bravely
insuefactos
well trained
perterriti
very terrified
imperiti
unskilled
alacritate ac studio
speed and zeal
consuerant
had been accustomed