how long was the wall around ancient jerusalem?

Answer 1

it depends in what period.
today the wall is about 1 km in eac direction, so it's about 4 km long.
in second temple period... the second wall and the external part of the first wall would have been about 6 km.
the 3rd wall would have been an extra 2-3 km.

in first temple period... the wall around the city of david would have been about 1-1.5 km, once the city was extended, it would have been around 3-4 km.

Answer 2

the wall is still partially there