The "popolari" or "popolani" are members of the "popolo" or people, sometimes opposed to the "Nobili," or old Nobility of birth, and sometimes to the "Grandi," or Magnates, the new nobility of wealth and status.
To be "placed under bounds" appears to mean banishment or confinement, under the form of a prohibition to cross certain stated "bounds."
The "Black" Cerchi are merely a branch of the Cerchi family: they were "Whites" politically.
Villani was well acquainted with Dante's works, and evidently regarded him as an authority. Therefore it must not be taken for granted, without further thought, that in every case of agreement Villani's testimony is an independent confirmation of Dante.
CHRONICLE
OF JOHN VILLANI
BOOK I.
This book is called the New Chronicle, in which many past things are treated of, and especially the root and origins of the city of Florence; then all the changes through which it has passed and shall pass in the course of time: begun to be compiled in the year of the Incarnation of Jesus Christ, 1300. Here begins the preface and the First Book.