Allobroges likewise, who had villages and possessions on the other side
of the Rhone, betake themselves in flight to Caesar and assure him that
they had nothing remaining, except the soil of their land. Caesar,
induced by these circumstances, decides that he ought not to wait until
the Helvetii, after destroying all the property of his allies, should
arrive among the Santones.

XII.--There is a river [called] the Saone, which flows through the
territories of the Aedui and Sequani into the Rhone with such incredible
slowness, that it cannot be determined by the eye in which direction it
flows. This the Helvetii were crossing by rafts and boats joined
together. When Caesar was informed by spies that the Helvetii had
already conveyed three parts of their forces across that river, but that
the fourth part was left behind on this side of the Saone, he set out
from the camp with three legions during the third watch, and came up
with that division which had not yet crossed the river. Attacking them,
encumbered with baggage, and not expecting him, he cut to pieces a great
part of them; the rest betook themselves to flight, and concealed
themselves in the nearest woods. That canton [which was cut down] was
called the Tigurine; for the whole Helvetian state is divided into four
cantons. This single canton having left their country, within the
recollection of our fathers, had slain Lucius Cassius the consul, and
had made his army pass under the yoke [B.C. 107]. Thus, whether by
chance, or by the design of the immortal gods, that part of the
Helvetian state which had brought a signal calamity upon the Roman
people was the first to pay the penalty. In this Caesar avenged not only
the public, but also his own personal wrongs, because the Tigurini had
slain Lucius Piso the lieutenant [of Cassius], the grandfather of Lucius
Calpurnius Piso, his [Caesar's] father-in-law, in the same battle as
Cassius himself.