Recognizing the enemy currently has the advantage and desperate to get the upper hand, you send scouts to look upstream for another way to cross. Sure enough, they find a practical ford.  You keep your fires bright and put your rearguard into place so the barbarians are fooled into thinking you plan on defending your camp in the morning. Then under the cover of night you march your army at the upstream ford and take a position on the far back of the Tagus.

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