Jericho is a very ancient city and it had high walls on several occasions long prior to the late bronze age, the period when the Israelite army is supposed to have caused the walls to fall. However, the city had been abandoned centuries before the time attributed to Joshua, and there were no walls for him to breach. Scholars say that at most there was just a small mud-brick village on the site of the former city. So, on the basis of archaeological evidence, it is not possible to state any dimensions for the walls during the fifteenth to thirteenth centuries BCE - the relevant period.
Most archaeologists agree that the perimeter of the Jericho wall was about 1/3 to 1/2 of a mile long.