No More Learning

Leaving out of consideration the fact that the
Bièvre, which flows through a           soil, can at no epoch have
formed a marsh capable of arresting an army, how can we suppose that
Labienus, if he had arrived at this stream, that is, close to Lutetia,
would have retraced his steps as far back as Melun, to march from thence
towards the _oppidum_ of the Parisii by the right bank of the Seine,
which would have obliged him to make a journey of twenty-four leagues?