Dalmatia ( theme ) The Theme of Dalmatia ( , " thema Dalmatias / Delmatias " ) was a Byzantine theme ( a military - civilian province ) on the eastern coast of the Adriatic Sea in Southeastern Europe , headquartered at Zadar . Origins . Dalmatia first came under Byzantine control in the 530s , when the generals of Emperor Justinian I ( r . 527 – 565 ) seized it from the Ostrogoths in the Gothic War . The invasions of the Avars and Slavs in the 7th century destroyed the main cities and overran much of the hinterland , with Byzantine control limited to the islands and certain new coastal cities such as Split and Dubrovnik , while Zara ( Zadar ) became the local episcopal and administrative center , under an " archon " . At the turn of the 8th to 9th century , Dalmatia was seized by Charlemagne ( r . 768 – 814 ) , but he returned it to the Byzantines in 812 , after the so - called " " Pax Nicephori " " . It is unclear whether the region was under actual rather than nominal Byzantine authority after that ; the local cities appear to have been virtually independent . Nevertheless , an " archon " of Dalmatia is mentioned in the 842 / 843 " Taktikon Uspensky " , and a seal of a " " strategos " of Dalmatia " dated to the first half of the century may indicate the existence of a Dalmatian theme , at least for a short time . History . The traditional date of the establishment of Dalmatia as a regular theme is placed in the early years of the reign of Emperor Basil I the Macedonian ( r . 867 – 886 ) , following the expeditions of Niketas Oryphas . Byzantium , the Roman Pope and the Franks vied for the support of the Slavs in Dalmatia ; in 878 , Zdeslav of Croatia was a noted Byzantine vassal , who deposed and was in turn deposed in a power struggle involving these powers . With the fall of the Carolingian Empire , the Franks ceased to be a major power in the Adriatic , while the Republic of Venice grew in power , beginning with Doge Pietro Tradonico . Around 923 , Tomislav of Croatia , the Byzantine Emperor and the two church patriarchs were involved a deal that transferred the control of the Byzantine Dalmatian cities to the new Croatian kingdom . This started a series of similar maneuvers and the Croatian – Bulgarian Wars , during which the Byzantine Emperors of the Macedonian dynasty maintained varying degrees of control over the Dalmatian cities . The Church also endured an analogous internal conflict between the rival dioceses of Split and Nin . The Venetian maritime power was obstructed by the Narentines and the Croats until Pietro II Orseolo who successfully intervened in 998 and 1000 , and arranged two important royal marriages with both the Croats and the Byzantines . Under Domenico I Contarini , Venice retook Zadar . Croatia had another period of control over the cities under Peter Krešimir IV , but the invasion of the Normans shifted the balance of power back to the Venetians . In the south , the city of Ragusa ( Dubrovnik ) , still under Byzantine control , started to grow in importance , and its Church diocese was elevated to an archbishopric in 998 . In the early 11th century , Byzantine control over Dalmatian cities started to be contested by the Serbian principality of Duklja , whose ruler Jovan Vladimir took control of Bar , near the border with the Theme of Dyrrhachium . His feats were repeated and bested by Stefan Vojislav twenty years later , and in 1034 , the Bar diocese was elevated to an archdiocese , but a war with Theophilos Erotikos soon followed . Stefan Vojislav ' s son Mihailo obtained papal support following the East – West Schism of 1054 , further weakening Byzantine influence in Dalmatia . Except for Dubrovnik and the southern third of Dalmatia , Byzantine control collapsed in the 1060s . Constantine Bodin pledged his support for Pope Urban II , which confirmed Bar ' s status as an archdiocese in 1089 , and resulted in a temporary demotion of the Ragusan diocese . By the end of the 11th century , the Kingdom of Hungary took the Kingdom of Croatia ' s place in controlling the northern Dalmatian hinterland . Duklja remained largely under Byzantine control , with a series of internal conflicts weakening its leaders . Byzantine predominance was restored under Emperor Manuel I Komnenos ( r . 1143 – 1180 ) , but vanished after his death and was replaced by Venetian control . With the rise of Stefan Nemanja , the Nemanjić dynasty took control of the lands in the south .