I thought it was a BUG that you could accidentally create a squad of Caravans.
I had been building Squads for my Army and forgot to turn it down and got 4 caravans (squad) in a group (non-breakable) I never did track their output though. (doh!)
Multiple (single) caravans moving between two (2) cities should be allowed if there are enough resource to support them and or to help offset one getting attacked leaving the route empty.
I would like to be able to assign more than one city as a destination when I create a Caravan. It seems reasonable that 1 Caravan could go to City A, then onto City B and then return to City C before starting the loop again.