The oldest chronicle of Venice, known as the Chronicon Sagornini, was compiled by deacon John, the chaplain and perhaps a relative of the Doge Pietro II Orseolo (991–1009).
John enjoyed the confidence of this doge, and was often sent as his ambassador to Holy Roman Emperors Otto III and Henry II.
In the first part of his chronicle, which deals with the early period of the republic, the narrative is often confused and deficient; later it becomes more accurate and complete, and for the time in which the writer himself lived it is particularly valuable.
[1]John's chronicle is a key primary source for the history of Slavic peoples and polities in Dalmatia during the 9th and 10th centuries, for which he probably drew on earlier documents.
[2] John reports on the troublesome dealings of Doge John (829–836) and his successor Peter (836–864) with the Neretva Slavs; the Pactum Lotharii of 840 and the Venetian-Frankish alliance against Slavic piracy; Domagoj and the wars about the Istrian region; the coup of the Slavic principality by Zdeslav; the usurper Branimir; and naval warfare against the Narentine Slavs in 887 and 948.