Duchy of Sermon

Sermon (Bulgarian and Serbian Cyrillic: Сермон; Greek: Σέρμων) was an 11th-century voivode (duke) of Syrmia and a local governor in the First Bulgarian Empire, vassal of Bulgarian emperor Samuil. His residence was in Sirmium (today Sremska Mitrovica, Serbia), where he produced his own golden coins.

Very little is known about him. Even his name may be simply a corruption of the name of Sirmium, added in the text of John Skylitzes in a later commentary. Sermon followed the Latin Rite, and was of Croatian origin. He had a brother, Nestongos, about whom nothing further is known, but who may have been an ancestor of the Nestongos aristocratic family that appears in Byzantium in the 11th–14th centuries.

Following the death of the Bulgarian Tsar Ivan Vladislav in early 1018, Bulgarian resistance against the Byzantine emperor Basil II collapsed. Basil therefore sent his generals to extend his control over the local lords of the northern and western Balkans. While most of them submitted and recognized the emperor's authority, Sermon refused. Consequently, the local Byzantine governor, Constantine Diogenes invited Sermon to a meeting at the estuary of the river Sava in the Danube, where each would only be accompanied by three attendants. Diogenes had hidden his sword in the folds of his clothes, and struck Sermon down. He then marched his army into Sirmium, taking possession of the town. Sermon's wife was sent as a captive to Constantinople, where she married a senior Byzantine official.

...
Wikipedia