Cephallenia ( theme ) The Theme of Cephallenia or Cephalonia ( , " thema Kephallēnias / Kephalonias " ) was a Byzantine theme ( a military - civilian province ) located in western Greece , comprising the Ionian Islands , and extant from the 8th century until partially conquered by the Kingdom of Sicily in 1185 . History . During the Roman Empire , the Ionian Islands ( Corfu , Cephalonia , Zakynthos , Ithaca , Leucas and Cythera ) were variously part of the provinces of Achaea and Epirus vetus . Except for Cythera , these formed the separate theme of Cephallenia . The islands remained largely unaffected by the Slavic invasion and settlement of the 7th century , and formed a base for the re - establishment of imperial control and the re - Hellenization of the mainland coast . It is unknown when exactly the theme of Cephallenia was established . Emperor Constantine VII Porphyrogennetos ( r . 913 – 959 ) affirms in his work , " De administrando imperio " , that it was originally a " tourma " ( a division ) of the theme of Longobardia in Southern Italy , and that it was raised to a " strategis " ( a " generalship " ) , but not a full theme , by Emperor Leo VI the Wise ( r . 886 – 912 ) . This is , however , clearly an error , for several instances of generals ( " strategoi " ) of Cephallenia are known through sources before that date . Thus , the " Taktikon Uspensky " of 842 / 843 clearly mentions a " strategos " of Cephallenia , and the Latin chronicle " Annales regni Francorum " mentions one already in 809 . A number of seals further push the establishment of the circumscription of Cephallenia , at least as a " strategis " if not as a theme , back to the middle or late 8th century . Constantine VII ' s confusion , however , reflects the close relation of Cephallenia with the imperial holdings in southern Italy : the Ionian Islands served as the main communication link with and staging base for operations in Italy , and defended the maritime approaches of the Ionian and Adriatic seas against Arab pirates . Contrary to Porphyrogennetos ' s account , Longobardia was probably initially constituted as a " tourma " of Cephallenia after the Byzantine recapture of Bari in 876 . Nevertheless , in several cases , the commands of Cephallenia and Longobardia ( or , alternatively , of Nicopolis on the Epirus mainland ) were thereafter held by the same person . The theme ' s " strategos " was probably based mostly at Cephallenia , but is also attested elsewhere , such as Corfu . In the " De administrando imperio " , the theme ranks seventh among the " Western " , or European themes ; as with all the European themes , its " strategos " did not receive his salary , 12 pounds of gold , from the imperial treasury , but was paid from his theme ' s tax revenue . Cephallenia was important chiefly in a maritime context , and had its own fleet , including a number of Mardaites as marines and rowers , under a " tourmarches " . Other " tourmarchai " and subordinate commanders headed the theme ' s army garrison . The historian Warren Treadgold conjecturally estimates the theme ' s military forces at some 2 , 000 men in the 9th century . The theme was also frequently used as a place of exile for political prisoners . The Theme of Cephallenia is frequently mentioned in military operations in the 9th – 11th centuries . In 809 , the " strategos " Paul defeated a Venetian fleet off Dalmatia . In 880 , the admiral Nasar heavily defeated an Arab pirate fleet that was plundering the theme ' s islands , and troops from Cephallenia subsequently participated in the Byzantine offensive in Italy . Mardaites from Cephallenia are then recorded in the failed expedition of 949 against the Emirate of Crete . The last mention of a " strategos " of Cephallenia comes in 1011 , when Kontoleon Tornikios was sent to Italy to quell a Lombard revolt . Following the collapse of Byzantine control in southern Italy in the mid - 11th century , the theme ' s importance declined , and it was headed by civilian governors , styled " krites " ( " judges " ) . From the late 11th century , the Ionian Islands became a battleground in the Byzantine – Norman Wars . The island of Corfu was held by the Normans in 1081 – 1085 and 1147 – 1149 , while the Venetians unsuccessfully besieged it in 1122 – 1123 . The island of Cephalonia was also unsuccessfully besieged in 1085 , but was plundered in 1099 by the Pisans and in 1126 by the Venetians . Finally , Corfu and the rest of the theme except for Leucas were captured by the Normans under William II of Sicily in 1185 . Although Corfu was recovered by the Byzantines by 1191 , the other islands henceforth remained lost to Byzantium , and formed a County palatine of Cephalonia and Zakynthos under William ' s Greek admiral Margaritus of Brindisi .