In the early 10th century, a prince ruling between the mouth of the Neretva and the hills of Herzegovina was simultaneously allied with Bulgaria, honoured by the Pope, and watched with suspicion by a Byzantine emperor. Nearly everything we know about the Zachlumians comes from a single book – and that book contradicts itself more than it first appears.
Anyone commissioning a map of the western Balkan coast in 10th-century Constantinople would have found a patchwork of small, loosely connected principalities. One of them is called, simply, "the Zachlumi" by the Byzantine emperor Constantine VII Porphyrogenitus in his handbook of statecraft, De Administrando Imperio – in modern terms, a principality in the lower Neretva valley and its mountainous hinterland, roughly between the area around Mostar and Stolac and the territory north of Dubrovnik. The name already surfaces in passing in chapter 30: Serbia, Pagania, "the so-called country of the Zachlumi," Terbounia and the country of the Kanalites are listed there as lands that, at various points, fell under the – mostly nominal – overlordship of the emperor. It is a brief aside, but it reveals how Constantinople viewed these coastal principalities: as loose satellites whose actual ties to the empire lagged far behind the diplomatic claim.
The real core of the surviving record, though, is chapter 33, which devotes its own, if brief, account to the Zachlumi. Together with a handful of Western sources, it is essentially all the contemporary text we have on this principality – which makes every single phrase in it both precious and treacherous.
Constantine first explains the name: "Zachlumi" (Ζαχλοῦμοι), he says, derives from a mountain called Chlumos ("Hum"); in Slavic the name roughly means "behind the mountain." He names two fortified places on this ridge, Bona and Chlum – more on those below. Then comes the claim that has been debated for generations: the current inhabitants of the land, Constantine states, are Serbs, descended from the time of that unnamed prince who once placed himself under the protection of Emperor Heraclius – the very same founding story he had already told for the Serbs proper. In other words, the Zachlumi are simply folded into the Serbian migration narrative, with no separate founder-figure or origin story recorded for their own land.
Only after that does the account turn concrete and contemporary: Constantine names a living ruler, "the anthypatos and patrikios Michael, son of Bouseboutzis, prince of the Zachlumi" – a man who was either still reigning when the text was compiled (around 945–950) or at least recent enough to be worth naming, and who holds two high-ranking Byzantine court titles. Those titles matter: Byzantium did not recognise Michael as an equal sovereign, but slotted him, at least on paper, into its own courtly hierarchy – a standard method Constantinople used to symbolically subordinate border princes it did not actually control.
This is where chapter 33 becomes genuinely interesting – and genuinely contradictory. Having just declared the Zachlumi as a people to be Serbs, Constantine then gives Prince Michael personally an entirely different lineage: his family, he writes, descends not from the Serbs but from an unbaptised people called the Litziki (Λιτζίκοι), settled on the river Vistula in the region of what is now Lesser Poland. Some scholars identify these Litziki with the Lendians (Lędzianie), a West Slavic group mentioned elsewhere in Constantine's work.
Constantine sums up this break as follows: Michael, son of Bouseboutzis, is prince of the Zachlumi – yet his ancestors did not descend from the Serbs but from that unbaptised people on the Vistula called the Litziki (our own close rendering of chapter 33).
What does this break in the middle of the text mean? The Serbian historian Tibor Živković has pointed out that the Vistula region in the 9th and 10th centuries was more plausibly associated with the "White Croats" than with "White Serbs" – which only deepens the puzzle. The Czech-American Slavist Francis Dvornik had already suggested the Zachlumi as a whole had a closer bond with the Croats than with the Serbs, since they seem to have migrated to the Balkans together with the Croats rather than the Serbs. The Croatian historian Neven Budak, meanwhile, cautions against projecting modern notions of ethnicity onto the early medieval period at all: belonging then was primarily a matter of political allegiance, not biological descent in our modern sense. The Romanian-American Byzantinist Florin Curta adds that Constantine's "Serb" label for these coastal principalities likely reflects the contemporary political overlordship of the Serbian prince Časlav – a snapshot of power around 950, not a reliable statement about 7th-century migration history.
Outside the emperor's handbook, Michael – also known as Mihailo Višević – first appears in 912, in an entirely different source: the chronicle of the Venetian deacon John (Chronicon Venetum). Pietro, son of the reigning Doge of Venice, was returning from a diplomatic mission to Constantinople when he fell into Michael's hands while travelling through Croatian and Zachlumian territory. The chronicler calls him "dux Sclavorum," a "prince of the Slavs" – Michael simply had the young man seized and sent on as a gift to the Bulgarian tsar Symeon I. It is a small, almost incidental episode, but it marks the decisive political alignment of these years: Michael tied himself firmly to Bulgaria.
That alliance explains Michael's next major appearance. The Serbian prince Petar Gojniković, a Bulgarian vassal since 897, had begun expanding westward – including toward the neighbouring Narentines of Pagania, bringing him into direct friction with Michael's own territory. According to Constantine, Michael, "his jealousy aroused," warned his Bulgarian ally Symeon of secret negotiations between Petar and Byzantium. Symeon responded with a campaign against Serbia, capturing Petar, who died in prison – an episode most scholars date to 917. In 924, Symeon placed Serbia under his direct rule, making Bulgaria Michael's immediate neighbour. Michael likely remained loyal to the Bulgarian tsar until Symeon's death in 927.
Running alongside this Bulgarian alliance is an entirely different strand of Michael's career: his relations with Rome and with the neighbouring Croatian kingdom. In 925, a church council was held in Split to cement the archbishopric's primacy over all of Dalmatia – alongside the touchy question of whether services should be held in Latin or in Slavonic, a dispute rooted in the legacy of Cyril and Methodius. The later Historia Salonitana of Archdeacon Thomas of Split, whose composition only began in the 13th century, preserves a letter from Pope John X to the Croatian king Tomislav, and notes that representatives of Michael also attended the council. That letter calls Michael "excellentissimus dux Chulmorum" – "most excellent duke of the Zahumljani." Whether this letter, in the form Thomas transmits it, is genuinely authentic or was later embellished is not conclusively settled among historians – a caution that applies to many documents from this early period.
Excellentissimus dux Chulmorum.
"Most excellent duke of the Zahumljani."Pope John X, letter of 925, preserved in Thomas of Split, Historia Salonitana (13th c.); own translation from the Latin
Some historians have read Michael's attendance at the council, together with the difference in titles between him and Tomislav (named "rex"), as evidence that Zahumlje was subordinate to the Croatian king at this time. John V. A. Fine disagrees: this was a church matter of pan-Dalmatian importance under papal authority, not evidence of political subordination. Fine also notes that in 926, when Croatia and Bulgaria went to war against each other, Michael stayed conspicuously neutral – a sign that he was trying to maintain good relations with both powers simultaneously. What Constantine VII himself leaves out is just as telling: he mentions neither the Split council nor, more strikingly, Michael's most consequential military action.
On 10 July 926, Western sources record, a ruler named "Michael, rex Sclavorum" seized the Byzantine port of Siponto in Apulia. Scholars now largely agree Michael was not acting as an imperial ally here but as Bulgaria's partner against Byzantine interests – a coastal raid in the middle of the Mediterranean, carried out by a prince whose core territory lay several hundred kilometres away. It shows that Zachlumian fleets on the Adriatic were seaworthy and formidable enough to strike far beyond their own coastline, a capability usually attributed to the neighbouring Narentines, whose piracy is feared in numerous Venetian and Frankish sources.
After 925, Michael's trail largely disappears from the surviving record. Fine suggests his reign may have continued into the 940s, based mainly on Constantine's mention of him, writing around 950, as a ruler apparently still current or at least worth naming. With Symeon's death in 927, Michael lost his most powerful patron, and some historians read his grand but ultimately powerless Byzantine court titles as the mark of a prince who, from then on, relied more on diplomatic skill than military strength.
Constantine's own explanation of the name – "behind the mountain" – can still be traced on the ground today. Mount Hum rises above the source of the Buna near Blagaj, not far from Mostar; the ancient Bona, named by Constantine as a stronghold, corresponds to this same area. On the later castle hill of Blagaj, building phases can be traced back to late antiquity, with a clearly identifiable expansion under Justinian in the 6th century; only after the 10th century did the site grow into a centre of the principality later known as Hum, with a princely court under the later-attested ruler Miroslav. The "za Hlmom" etymology – "behind the hill" – is considered plausible by scholars and is, at its core, already the explanation Constantine himself gives, but it naturally cannot be checked independently of his own account; it remains a linguistically convincing, but ultimately unprovable, toponymic interpretation.
Travelling through the same landscape near Stolac, one also encounters the impressive ruins of Daorson, the fortified capital of the Illyrian Daorsi tribe, with its monumental cyclopean walls dating from the 4th to the 1st century BC. It is a tempting archaeological landmark – but a full millennium older than Michael and his Zachlumi, with no documented continuity into the Slavic settlement of the area. The Bosnian archaeologist and historian Pavao Anđelić, whose studies on the territorial organisation of medieval Bosnia engaged closely with the historical topography of the Hum region, himself warned against too hastily blending pre-Slavic and early Slavic sites in this densely settled river landscape.
After Michael, the sources never again coalesce into a comparably clear picture. Časlav, the Serbian prince who took power after Symeon's death, may have laid claim to parts of Zachlumian territory, yet Constantine himself, writing around 950, still lists Zachlumia explicitly as a separate polity – a sign that, at least within the emperor's lifetime, no complete absorption had yet taken place. Only over the following century and a half did the territory, increasingly called "Hum," pass back and forth between Croatian, Bosnian and Serbian spheres of influence, until it was finally absorbed into larger neighbouring realms during the 12th century – a long, uneven process that already lies well beyond the narrower subject of this article, the early medieval principality of the 9th and 10th centuries.
What remains is the picture of a small coastal principality that held its own with remarkable skill between far larger powers – Byzantium, Bulgaria, the papacy, the Croatian and Serbian princely houses – for as long as a shrewd operator like Michael Višević was at the helm. And what remains, too, is a reminder of how much of our entire knowledge of such principalities hangs on a single, internally contradictory chapter of an imperial handbook. It is precisely these fractures in the text – the double lineage, the silence on Siponto, the doubtful papal letter – that make the Zachlumians a lesson in how carefully early medieval sources must be handled, and how vivid the stories behind them remain all the same.
The Narentines · The Croats · The Serbs · The Travunians.
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