Miscellaneous Notes on Byzantine Istria and the Slav Presence
"L'Istria bizantina ed alcuni problemi del Placito di Risano." In Slovenia in sosednje dezele med antiko in karolinsko dobo. Začetki slovenske etnogeneze. Ed. by R. Brato. (Ljubljana: Narodni Muzej Slovenije, 2000), pp. 81-95.
From: Southeastern Europe in the Middle Ages, 500-1250 by Florin Curta,
The Slavic raid of 610 on Istria, until then under Byzantine control, is mentioned in Paul the Deacon's History of the Lombards as following an Avar attack on northeastern Italy.
[Paul the Deacon, History of the Lombards IV.40, ed. by G. Waitz (Hanover: Hahnsche Buchhandlung, 1878), p. 168. At this point of his History, Paul relied on information borrowed from the now lost history of Secundus of Trento. See K. Gardiner, "Paul the Deacon and Secundus of Trento," in History and Historians in Late Antiqutiy, ed. by B. Croke and A. Emmett (Sydney: Pergamon Press, 1983), pp. 147-154.]
Relying on information borrowed from an earlier source, Paul the Deacon mentions in a single breath the Avar conquest of Forum Iulii in Italy and the devastation of Istria by the Sclavenes. [Same citation.]
...Occupied by Roman troops during the Gothic wars in Italy at some point between 535 and 544, the [Istrian] peninsula remained under their direct control until the Lombard conquest of the mid-eighth century. Under the authority of the exarch of Ravenna, Istria was by the late seventh century a separate administrative unit, much like a kleisura, with its own troops under the command of a local magister militum. As in contemporary Italy, a line of small forts stretching across the northern half of the peninsula was designed to control access from Lombard or  Avar-held territory to the north. The Istrian troops must have been relatively numerous, given that some of them participated in crushing the usurpation of imperioal power in the aftermath of Emperor Constans II's assassination in Sicily (669). They were stationed in forts on the northern frontier of the province, as evidenced by a number of cemeteries extending from the the sixth to the eighth century. (67) Many such cemeteries associated with neighboring forts produced stone-lined graves of men with weapons - short swords, axes, and arrowheads. Side by side with their burials, archaelogists found a relatively large number of child burials, as well as double burials, often including female skeletons. This suggests that the occupation of the northern Istrian forts [hillforts?] was of a permanent character and that soldiers lived there together with their families. In Mejica [where is this?], the excavated 260 burials, many of which were dated to the seventh century, point to the existence of about 60 individuals per generation. As many as six families with accompanying clients may have occupied the fort at any one time during that century. Cemeteries were not associated with any funerary chapels or churches, but during the seventh and eighth centuries several churches were built in the countryside of Byzantine Istria. the province had three episcopal sees (Tergeste/Triest, Parentium/Poreč, and Pola/Pula), and the presence of the Istrian bishops is documented at the Lateran council of 649, as well as at the Sixth Ecumenical Council of 680/1. An early ninth-century source know as the placitum of Riana describes the local Byzantine administration in existence before the Frankish take-over as consisting of consuls, tribunes, domestici, vicari, and lociservatores. According to the declaration recorded in the placitum, the central government in Constantinople used to exact taxes from the Istrian cities and their hinterland in the amount of 344 gold coins. Local bishops paid half of that amount and the incumbent durities, an indication of their power and influence. (68)
 For a short while between the mid-seventh century and Charlemane's destruction of the Lombard kingdom in 774, Istria was controlled by the Lombards, but a letter of Patriarch John of Grado to Pope Stephen III describes the hostilities of the Istrians towards Lombards and their loyalty to Byzantium. Following the implementation of Carolingian rule, the local aristocrats were also concerned with maintaining the social and political practicies that have been in use during the Byzantine era, as clearly attested by the placitum of Riana. It is only under Frankish rule, in the early ninth century, that the presence of Slavs is first attested, a phenomenon linked to the appearance of a new group of burials in northern Istria, well illustrated by the cemetery at Predloka (near Koper, in northwestern Istria), with good analogies in late eighth-century burials in northern Slovenia and Carinthia. This suggests a migration from neighboring Carantania, perhaps of people fleeing the country in the circumstances surrounding the revolts of the local aristocracy during and after the brief reign of Chietmar.
The picture of Dark Age Istria is similar in many respects to that of the contemporary Dalmatian coast, Albania, and Greece, for which there is nevertheless less information from written sources. Beginning with the late sixth century, the western Balkans seem to have experienced a much earlier phase of that transformation of the settlement pattern known as incastellamento. With the complete abandonment of dispersed rural sites of Roman or pre-Roman origin, the population shrank to diminutive dimensions during the Dark Ages. Occupation was now restricted to a number of hilltop forts, such as Pogradec, Kruja, and Sarda in the vicinitz of Dyrrachium (present-day Durrës, in Albania), with a layout and social structure very different from the previous urban and rural settlements. (69) However, such forts served as a primarily military purpose, namely to monitor key passes through the mountains separating the coastal region from the interior of the peninsula. The system in existence in Dalmatia is described in chapter 29 of Emperor Constantine VII Porphyrogenitus' De administrando imperio: "For near the sea, beneath that sme city [i.e., Spalato], lies a city called Salona, which is  half as large as Constantinoble, and here all the Romani would muster and be equipped and thence start out and come to the frontier pass (kleisoura), which is four miles from this very city, and is called Kleisa to this day, from its closing in those who pass that way. (70, not available) The kleusoura apparently closed access from across an unknown river, perhaps the neighboring Cetina. Like the kleisourai of Istria and the Struma valley, Kleisa may have been designed to prevent attacks on the coastal cities and roads by "Slavs on the far side of the river, who were also called Avars." (71, not available)
68. The placitum of 804 has been published with extensive commentaries by A. Petranović and A. Margetić, "Il Placito del Risano," Atti. Centro di ricerche storiche - Rovigno, vol. 14 (1983-1984), pp. 55-75. See also A. Guillou, "La présence byzantine dans les pays du nord de l'Adriatique. Un champ des mutations socio-économiques," Byzantina, vol. 13 (1985), p. 311; L. Margetić, "L'Istria bizantina ed alcuni problemi del Placito di Risano," in Slovenia in sosednje dezele med antiko in karolinsko dobo. Začetki slovenske etnogeneze. Ed. by R. Brato. (Ljubljana: Narodni Muzej Slovenije, 2000), pp. 81-95.
69. The Dark Age incastellamento in the Balkans may explain why in both Romanian (a Romance Language) and Albanian (a non-Romance language) the term in use for fort (cetate and qytet, respectively) derives from the Latin word for city (civitas). See M. Pillon, "Sémantique et histoire de l'habitat> le fossatum proto-byzantin, le fshat albanais et le sat roumain," Erytheia, vol. 14 (1993), pp. 26-27.