Please could you tell me how many miles/kilometres separate Ravenna
from Pisa? To be picky, it would make sense if it was estimated on
roads shown on a map not later than 1821, as I am interested in
tracing a journey that was made at that time.

antonyp32,
Never having had the pleasure of touring Italy (but having read about
it) it is likely your traveller of 1821 would have gone North West
from Ravenna (Province of Emilia Romagno) for 45 miles (passing a
mountain range that streatchs for much of Italy towards the South),
then turned South West, passing through Bologne in a near straight
line eventually arriving at Pisa (in Tuscany). Total distance
estimated at 130 miles.

Maps used are; composite map made in 1923 set in 1494. See here:
http://www.lib.utexas.edu/maps/historical/shepherd/italy_1494_shepherd.jpg
& also one made in 1882 following the same route. See here:
http://www.lib.utexas.edu/maps/historical/italy_world_atlas_1882.jpg

Method used was a piece of string and comparison between the two maps.
Other historic maps on Italy are available here:
http://www.lib.utexas.edu/maps/italy.html

Kind regards
gfmaster