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 Longest city walls 

What about Genoa (Italy) fortifications?
There is an article on Italian wikipedia, but there is no mention about them on the (much richer and exhaustive) English version!
The complete circle of the Genoese ""Mura nuove"" (""New"" since they were built between 1626 and 1639, while, for comparison, the oldest one or the remaining four progressively expanding sets were built before the year 1000) is longer then 20 kilometers.

OP
78.6.21.50  "