Olympia: The Age of Gods PBEM (May 4 1999)
Swamps, bogs and pits are so difficult to negotiate that they present special difficulties for the traveller.
No stack may move at riding speed into or inside a swamp province, or into a bog or pit. At best, a stack can move a walking pace.
If a stack contains animals, the difficult terrain will further slow travel by an extra day. A wagon is considered an animal because of its horses.