, ▁the ▁boundaries ▁of ▁the ▁theme ▁fl uct u ated ▁along ▁with ▁the ▁northern ▁front ier ▁of ▁By z ant ium ▁during ▁the ▁By z antine – B ul gar ian ▁Wars . ▁Initial ly , ▁the ▁theme ▁must ▁have ▁compr ised ▁most ▁of ▁the ▁ancient ▁Dioc ese ▁of ▁Th race , ▁except ▁for ▁the ▁country ▁along ▁the ▁Dan ube ▁over run ▁by ▁the ▁Bulg ars ▁( Lower ▁Mo esia ), ▁but ▁after ▁the ▁con quest s ▁of ▁K rum ▁( r . ▁ 8 0 3 – 8 1 4 ), ▁Om ur tag ▁( r . ▁ 8 1 4 – 8 3 1 ), ▁and ▁Sym e on ▁( r . ▁ 8 9 3 – 9 2 7 ) ▁the ▁border ▁moved ▁by ▁stages ▁south ▁of ▁the ▁B alk an ▁mountains ▁to ▁roughly ▁the ▁line ▁of ▁the ▁present ▁Bulgar ian ▁front ier ▁with ▁Greece ▁and ▁Turkey . ▁Thus , ▁at ▁around ▁the ▁start ▁of ▁the ▁t enth ▁century , ▁the ▁theme ▁compr ised ▁essentially ▁the ▁eastern ▁half ▁of ▁modern ▁Eastern ▁Th race , ▁although ▁it ▁extended ▁north ▁along ▁the ▁coast ▁to ▁include ▁An ch ial os . ▁ ▁From ▁the ▁ele vent h ▁century , ▁Th race ▁and ▁Mac ed onia ▁appear ▁to ▁have ▁been ▁usually ▁combined , ▁as ▁att ested ▁by ▁numerous ▁strateg oi ▁and ▁jud ges ▁( k rit ai ' ') ▁holding ▁juris diction ▁over ▁both ▁them es . ▁The ▁name ▁fell ▁out ▁of ▁use ▁as ▁an ▁administrative ▁term ▁in ▁the ▁Pal ai olog an ▁period