 Despite all these measures , the Empire suffered several major setbacks in the course of the 6th century . The first one was the plague , which lasted from 541 to 543 and , by decimating the Empire 's population , probably created a scarcity of labor and a rising of wages . The lack of manpower also led to a significant increase in the number of " barbarians " in the Byzantine armies after the early 540s . The protracted war in Italy and the wars with the Persians themselves laid a heavy burden on the Empire 's resources , and Justinian was criticized for curtailing the government @-@ run post service , which he limited to only one eastern route of military importance . 
