Theme ( Byzantine district ) The themes or themata ( ; singular θέμα , " thema " ) were the main administrative division s of the middle Byzantine Empire . They were established in the mid - 7th century in the aftermath of the Muslim conquests of parts of Byzantine territory , and replaced the earlier provincial system established by Diocletian and Constantine the Great . In their origin , the first themes were created from the areas of encampment of the field armies of the East Roman army , and their names corresponded to the military units that had existed in those areas . The theme system reached its apogee in the 9th and 10th centuries , as older themes were split up and the conquest of territory resulted in the creation of new ones . The original theme system underwent significant changes in the 11th and 12th centuries , but the term remained in use as a provincial and financial circumscription , until the very end of the Empire . History . Background . During the late 6th and early 7th centuries , the Eastern Roman Empire was under frequent attack from all sides . The Sassanid Empire was pressing from the east on Syria , Egypt , and Anatolia . Slavs and Avars raided Greece and settled in the Balkans . The Lombards occupied northern Italy , largely unopposed . In order to face the mounting pressure , in the more distant provinces of the West , recently regained by Justinian I ( r . 527 – 565 ) , Emperor Maurice ( r . 582 – 602 ) combined supreme civil and military authority in the person of an " exarch " , forming the exarchates of Ravenna and Africa . These developments overturned the strict division of civil and military offices , which had been one of the cornerstones of the reforms of Diocletian ( r . 284 – 305 ) . In essence however they merely recognized and formalized the greater prominence of the local general , or " magister militum " , over the respective civilian praetorian prefect as a result of the provinces ' precarious security situation . This trend had already featured in some of the administrative reforms of Justinian I in the 530s . Justinian had given military authority to the governors of individual provinces plagued by brigandage in Asia Minor , but more importantly , he had also created the exceptional combined military - civilian circumscription of the " quaestura exercitus " and abolished the civilian Diocese of Egypt , putting a " dux " with combined authority at the head of each of its old provinces . However , in most of the Empire , the old system continued to function until the 640s , when the eastern part of the Empire collapsed under the onslaught of the Muslim Caliphate . The rapid Muslim conquest of Syria and Egypt and consequent Byzantine losses in manpower and territory meant that the Empire found itself struggling for survival . In order to respond to this unprecedented crisis , the Empire was drastically reorganized . The remaining imperial territory in Asia Minor was divided into four large themes , and although some elements of the earlier civil administration survived , they were subordinated to the governing general or " stratēgos " . Origins . The origin and early nature of the themes has been heavily disputed amongst scholars . The very name " thema " is of uncertain etymology : it has been suggested that it came from the Chazar Turkic " tūmān " , " ten thousand men " , but most scholars follow Constantine Porphyrogennetos , who records that it originates from Greek " thesis " ( " placement " ) . The date of their creation is also uncertain . For most of the 20th century , the establishment of the themes was attributed to the Emperor Heraclius ( r . 610 – 641 ) , during the last of the Byzantine – Sassanid Wars . Most notable amongst the supporters of this thesis was George Ostrogorsky who based this opinion on an extract from the chronicle of Theophanes the Confessor mentioning the arrival of Heraclius " in the lands of the themes " for the year 622 . According to Ostrogorsky , this " shows that the process of establishing troops ( themes ) in specific areas of Asia Minor has already begun at this time . " This view has been objected to by other historians however , and more recent scholarship dates their creation later , to the period from the 640s to the 660s , under Constans II ( r . 641 – 668 ) . It has further been shown that , contrary to Ostrogorsky ' s conception of the " themata " being established from the outset as distinct , well - defined regions where a " stratēgos " held joint military and civil authority , the term " thema " originally seems to have referred exclusively to the armies themselves , and only in the later 7th or early 8th centuries did it come to be transferred to the districts where these armies were encamped as well . Tied to the question of chronology is also the issue of a corresponding social and military transformation . The traditional view , championed by Ostrogorsky , holds that the establishment of the themes also meant the creation of a new type of army . In his view , instead of the old force , heavily reliant on foreign mercenaries , the new Byzantine army was based on native farmer - soldiers living on state - leased military estates . More recent scholars however have posited that the formation of the themes did not constitute a radical break with the past , but rather a logical extension of pre - existing , 6th - century trends , and that its direct social impact was minimal . First themes : 640s – 770s . What is clear is that at some point in the mid - 7th century , probably in the late 630s and 640s , the Empire ' s field armies were withdrawn to Anatolia , the last major contiguous territory remaining to the Empire , and assigned to the districts that became known as the themes . Territorially , each of the new themes encompassed several of the older provinces , and with a few exceptions , seems to have followed the old provincial boundaries . The first four themes were those of the Armeniacs , Anatolics and Thracesians , and the Opsician theme . The Armeniac Theme ( , " Thema Armeniakōn " ) , first mentioned in 667 , was the successor of the Army of Armenia . It occupied the old areas of the Pontus , Armenia Minor and northern Cappadocia , with its capital at Amasea . The Anatolic Theme ( , " Thema Anatolikōn " ) , first mentioned in 669 , was the successor of the Army of the East ( , " Anatolē " ) . It covered southern central Asia Minor , and its capital was Amorium . Together , these two themes formed the first tier of defence of Byzantine Anatolia , bordering Muslim Armenia and Syria respectively . The Thracesian Theme ( Θέμα Θρᾳκησίων , " Thema Thrakēsiōn " ) , first mentioned clearly as late as c . 740 , was the successor of the Army of Thrace , and covered the central western coast of Asia Minor ( Ionia , Lydia and Caria ) , with its capital most likely at Chonae . The Opsician Theme ( , " Thema Opsikiou " ) , first mentioned in 680 , was constituted from the imperial retinue ( in Latin " Obsequium " ) . It covered northwestern Asia Minor ( Bithynia , Paphlagonia and parts of Galatia ) , and was based at Nicaea . Uniquely , its commander retained his title of " komēs " ( " count " ) . In addition , the great naval division of the Carabisians or " Karabisianoi " ( Kαραβισιάνοι , from κάραβις , " ship " ) , first mentioned in 680 , was probably formed of the remains of the Army of the Illyricum or , more likely , the old " quaestura exercitus " . It never formed a theme proper , but occupied parts of the southern coast of Asia Minor and the Aegean Islands , with its " stratēgos " seat most likely at Samos . It provided the bulk of the Byzantine navy facing the new Arab fleets , which after the Battle of the Masts contested control of the Mediterranean with the Empire . In the event , the Carabisians would prove unsatisfactory in that role , and by 720 they had been disbanded in favour of a fully - fledged naval theme , that of the Cibyrrhaeots ( , " Thema Kibyrrhaiotōn " ) , which encompassed the southern coasts of Asia Minor and the Aegean islands . The part of the region of Thrace under Byzantine control was probably constituted as a theme at about 680 , as a response to the Bulgar threat , although for a time the command over Thrace appears to have been exercised by the Count of the " Opsikion " . Successive campaigns by the emperors of the Heraclian dynasty in Greece also led to the recovery of control of Central Greece from Slavic invaders , and to the establishment of the theme of Hellas there between 687 and 695 . Sicily too was formed as a theme by the end of the 7th century , but the imperial possessions in mainland Italy remained under the exarch of Ravenna or the local " doukes " , as did Byzantine Africa until the fall of Carthage in 698 . At the same time , Crete and the imperial exclave of Cherson in the Crimea formed independent " archontia i " . Thus , by the turning of the century , the themes had become the dominant feature of imperial administration . Their large size and power however made their generals prone to revolt , as had been evidenced in the turbulent period 695 – 715 , and would again during the great revolt of Artabasdos in 741 – 742 . The suppression of Artabasdos ' revolt heralded the first significant changes in the Anatolian themes : the over - mighty " Opsikion " was broken up with the creation of two new themes , the Bucellarian Theme and the Optimates , while the role of imperial guard was assumed by a new type of professional force , the imperial " tagma ta " . Height of the theme system , 780s – 950s . Despite the prominence of the themes , it was some time before they became the basic unit of the imperial administrative system . Although they had become associated with specific regions by the early 8th century , it took until the end of the 8th century for the civil fiscal administration to begin being organized around them , instead of following the old provincial system . This process , resulting in unified control over both military and civil affairs of each theme by its " strategos " , was complete by the mid - 9th century , and is the " classical " thematic model mentioned in such works as the " Klētorologion " and the " De Administrando Imperio " . At the same time , the need to protect the Anatolian heartland of Byzantium from the Arab raids led to the creation , in the later 8th and early 9th centuries , of a series of small frontier districts , the " kleisourai " or " kleisourarchiai " ( " defiles , enclosures " ) . The term was previously used to signify strategically important , fortified mountain passages , and was now expanded to entire districts which formed separate commands under a " kleisourarchēs " , tasked with guerrilla warfare and locally countering small to mid - scale incursions and raids . Gradually , most of these were elevated to full themes . Transformation and decline of the theme system , 960s – 1070s . With the beginning of the Byzantine offensives in the East and the Balkans in the 10th century , especially under the warrior - emperors Nikephoros II ( r . 963 – 969 ) , John I Tzimiskes ( r . 969 – 976 ) and Basil II ( r . 976 – 1025 ) , newly gained territories were also incorporated into themes , although these were generally smaller than the original themes established in the 7th and 8th centuries . At this time , a new class of themes , the so - called " minor " ( ) or " Armenian " themes ( ) appear , which Byzantine sources clearly differentiate from the traditional " great " or " Roman " themes ( ) . Most consisted merely of a fortress and its surrounding territory , with a junior " stratēgos " ( called " zirwar " by the Arabs and " zoravar " by the Armenians ) as a commander and about 1 , 000 men , chiefly infantry as their garrison . As their name reveals , they were mostly populated by Armenians , either indigenous or settled there by the Byzantine authorities . One of their peculiarities was the extremely large number of officers ( the theme of Charpezikion alone counted 22 senior and 47 junior " tourmarchai " ) . While well suited for defence , the " Armenian " themes were incapable of responding to major invasions or undertake sustained offensive campaigns on their own . Thus , from the 960s , more and more professional regiments , both from the old " tagmata " and newly raised formations , were stationed along the border . To command them as well as coordinate the forces of the small frontier themes , a number of large regional commands ( " ducates " or " catepanates " ) , under a " doux " or " katepano " , were set up . In the East , the three original such commands , set up by John Tzimiskes , were those of the " doukes " of Antioch , Chaldia and Mesopotamia . As Byzantium expanded into Greater Armenia in the early 11th century , these were complemented or replaced by the commands of Iberia , Vaspurakan , Edessa and Ani . In the same vein , the " Armenian " themes seem to have been placed under a single " strategos " in the mid - 11th century . The series of soldier - emperors culminating in Basil II led to a situation where by 1025 Byzantium was more powerful than any of its enemies . At the same time , the mobile , professional forces of the " tagmata " gained in importance over the old thematic armies ( and fleets ) of the interior , which soon began to be neglected . Indeed , from the early 11th century military service was increasingly commuted to cash payments . While the frontier ducates were able to meet most local threats , the dissolution of the old theme - based defensive system deprived the Byzantine defensive system of any strategic depth . Coupled with increasing reliance on foreign mercenaries and the forces of allied and vassal states , as well as the revolts and civil wars resulting from the widening rift between the civilian bureaucracy in Constantinople and the land - holding military elites ( the " dynatoi " ) , by the time of the Battle of Manzikert in 1071 , the Byzantine army was already undergoing a severe crisis and collapsed completely in the battle ' s aftermath . Organization . The term " thema " was ambiguous , referring both to a form of military tenure and to an administrative division . A theme was an arrangement of plots of land given for farming to the soldiers . The soldiers were still technically a military unit , under the command of a strategos , and they did not own the land they worked as it was still controlled by the state . Therefore , for its use the soldiers ' pay was reduced . By accepting this proposition , the participants agreed that their descendants would also serve in the military and work in a theme , thus simultaneously reducing the need for unpopular conscription as well as cheaply maintaining the military . It also allowed for the settling of conquered lands , as there was always a substantial addition made to public lands during a conquest . The commander of a theme , however , did not only command his soldiers . He united the civil and military jurisdictions in the territorial area in question . Thus the division set up by Diocletian between civil governors ( " praesides " etc . ) and military commanders ( " duces " etc . ) was abolished , and the Empire returned to a system much more similar to that of the Republic or the Principate , where provincial governors had also commanded the armies in their area . The following table illustrates the thematic structure as found in the Thracesian Theme , c . 902 - 936 : List of the themes between c . 660 and 930 . This list includes the large " traditional " themes established in the period from the inception of the theme system in c . 660 to the beginning of the great conquests in c . 930 and the creation of the new , smaller themes . Notes : < br > List of new themes , 930s – 1060s . These were the new major or minor themes , the so - called " Armenian " themes or generalships ( " strategiai " ) , established during the Byzantine conquests , both in the East and in the Balkans .