The route could always be retraced if it was the wrong one.
He accompanied them on their return, by way of the Casiquiare canal, and afterwards retraced his route to the Orinoco.
He marched to the neighbourhood of Constantinople, but finding himself unable to undertake the siege of that superbly strong city, he retraced his steps westward and then marched southward through Thessaly and the unguarded pass of Thermopylae into Greece.
After these failures Caesar determined to take no active part in politics for a time, and retraced his steps to the East in order to study rhetoric under Molon, at Rhodes.
In carrying out this scientific procedure false steps will from time to time be made, which will have to be retraced, or rather amended; but the combination of experimental science with theory has elevated our presumption of the rationality of all natural processes, so far as we can apprehend them at all, into practical certainty; so that, though the mode of presentation of the results may vary from age to age, it is hardly conceivable that the essentials of the method are not of permanent validity.