The Emperor has decreed that the speed limit for horses and horse-drawn vehicles within city limits is to be 5 leagues per hour. As usual he has left the implementation details to his Scientific Adviser.
Using only medieval-type measuring devices, how can the Adviser satisfy the Emperor's wishes?
You can assume that there are wooden odometers available
and medieval clocks
It presumably doesn't make any difference to the answer but a league can be assumed to be 3 miles.