▁Emperor ▁Const antine ▁IV ▁was ▁ups et ▁and ▁led ▁an ▁army ▁to ▁prevent ▁the ▁Bulg ars ▁from ▁remaining ▁there . ▁The ▁By z antine ▁expedition ▁against ▁the ▁Bulg ars ▁ended ▁dis astr ously ▁and ▁after ▁defe ating ▁the ▁imperial ▁forces , ▁As par uk h ▁forced ▁the ▁nearby ▁S lav ic ▁tribes ▁to ▁pay ▁t ribute ▁to ▁him , ▁while ▁leaving ▁their ▁trib al ▁organization ▁int act . ▁As ▁a ▁result ▁of ▁this ▁defeat , ▁the ▁emp ire ▁was ▁forced ▁to ▁sign ▁a ▁treat y ▁recogn izing ▁the ▁Bulgar ▁state ▁in ▁ 6 8 1 . ▁Despite ▁the ▁area ▁having ▁been ▁for ▁some ▁time ▁under ▁the ▁de ▁fact o ▁control ▁of ▁various ▁S lav ic ▁tribes , ▁the ▁em per ors ▁of ▁By z ant ium ▁had ▁kept ▁up ▁the ▁fiction ▁that ▁the ▁area ▁was ▁still ▁imperial , ▁as ▁up ▁to ▁ 6 8 1 ▁no ▁true ▁state ▁had ▁replaced ▁imperial ▁rule . ▁This ▁was ▁the ▁first ▁time ▁that ▁the ▁By z antine ▁emp ire ▁officially ▁acknowled ged ▁another ▁state ▁in ▁the ▁B alk ans . ▁▁ 6 8 1 - 8 9 3 ▁Pl iska ▁was ▁the ▁capital ▁of ▁the ▁First ▁Bulgar ian ▁Empire ▁between ▁ 6 8 1 ▁and ▁ 8 9 3 ▁AD . ▁According ▁to ▁a ▁Bulgar ian ▁chron icle , ▁it ▁was ▁founded ▁by ▁Khan ▁As par uk h . ▁At ▁its ▁greatest ▁extent , ▁it ▁had ▁an ▁area ▁of ▁ 2 1 . 8   km ² ▁and ▁was ▁surrounded ▁by ▁ear then ▁r amp arts .