I think a shade-in would be very appropriate.  I discovered an article which gives the line of the Bugar-Byzantine border (also demarcated by "The Great Fence") in the time of Khagan Omurtag: From Develtus to Makrolivada (now Gara Zlati Dol) on the Maritza River thence to a fortress towards the mountains NORTH of Philippopolis (ie this city was Byzantine).  This can be found at: 

  http://ehr.oxfordjournals.org/cgi/reprint/XXV/XCVIII/276.pdf