Final answer:
They crossed the river by using a ferry, which is one of the various traditional methods people have utilized throughout history for river crossings when bridges or fords were not available.
Step-by-step explanation:
When they couldn't walk across the bridge, the individuals in question got across the river by entering the gates of the ferry and crossing from shore to shore. Historical accounts and the significance of rivers in transportation highlight various methods people used to cross rivers. Fords were shallow places where rivers could be crossed without the need for a vessel, but bridges and pontoons later provided more stable crossing points.
The reference to the ferry indicates that when a bridge was not an option, ferries served as an alternative means to transport people and goods across water bodies. Moreover, the necessity and ingenuity in river crossings are evident through history, from the use of fords and bridges in settlement names to the construction of temporary pontoons during military campaigns or the use of ferries for everyday commutes.