Commentary Purg VI 127-129

The fifth and final apostrophe is, naturally, of Florence herself, and is, naturally, dripping with sarcasm, reminiscent of the earlier apostrophe that opens Inferno XXVI, in which the city is asked to rejoice in her renown for having produced so many thieves who now disport themselves in hell.  For the supposedly 'digressive' nature of Dante's remarks, see C.Purg.VI.76-77.