Vol. 2: A 804 usque ad 1077
Between 905 and 911, usually dated to 910.

Pope Sergius III writes to John, the bishop of Pula, informing him of Archbishop of Ravenna John XI's complaints against Count Albuin, who unlawfully alienated the possessions of the Church of Ravenna in Istria, and asking him to personally convey to the Count that he must return these possessions under the threat of excommunication and that King Berengar I will not be crowned emperor until he grants Albuin’s March (of Istria or of Friuli) to someone better.

B = A rotulus, presumably from the 10th century, that is nowadays considered lost. It was lithographed and transcribed by Antonio Maria Ceriani and Giulio Porro (cited below).
Previous Editions
Antonio Maria Ceriani and Giulio Porro, Il rotolo opistografo del principe Antonio Pio di Savoia (Milan 1882), p. 26 (= Archivio storico lombardo 11 (1884): p. 31); based on B.
Samuel Löwenfeld, “Acht Briefe aus der Zeit König Berengars: Gedruckt und erlaütert in ‘Ceriani e Porro, Il rototo opistografo del principe Antonio Pio di Savoja’ aus dem Italienischen mit eigenen Bemerckungen,” Neues Archiv der Gesellschaft für ältere deutsche Geschichtskunde 9 (1884): pp. 537–38; based on Ceriani-Porro's edition.
Harald Zimmermann (ed.), Papsturkunden 896–1046, vol. 1: 896–996 (Vienna 1984), doc. 30, pp. 52–53; adapted replica of Löwenfeld’s edition.
FIM Edition
Adapted replica of Ceriani–Porro's edition with Zimmermann’s emendations reported in the critical apparatus.

(SC) Sergius episcopus servus servorum Dei, reverentissimo et sanctissimo confratri nostro Iohanni Polensi episcopo.

Iampridem per nostras apostolicas litteras admonendo mandavimus Albuinum comitem pro rebus et familiis reverentissimi et sanctissimi confratris nostri Iohanni[s]a Ravennatis archiepiscopi, ut nulla[m] molestia[m]b nullamque contrarietatem in eis fecisset nec in ipsis nec in rebus sancti Petri, quas ei per preceptum concessimus.

Nunc autem cognovimus per missum eiusdem confratris nostri archiepiscopi, quod ipse Albuinus multa mala in easdem res faciatc et etiam in suos vasallos illas dedit, precipue eam quae fuit sanctae nostrae Ecclesiae.

Unde sanctitati tue mandamus, ut ad eum presentaliterd vadas et moneas illum ex nostra parte, ut absque mora hec omnia emendare faciat et quicquid inde tulit reddere faciat.

Et si non fecerit, sapiat certissime, quia mittemus illum extra Ecclesiam et sub anathemate eum damnabimus, scribentes patriarche et omnibus episcopis confratribus nostris ut eum non recipiant, et insuper Berengarius rex non accipiet a nobis coronam donec promittat, ut tollat Albuino ipsam Marcam et det eam alteri moliorie quam ipse est.

Critical apparatus

asic Iohanni B; Iohannis em. Zimmermann.  b) nulla molesta B; em. Zimmermann.  c) et quicquid inde tullit add. al. man. sup. l. B.  dsic B; personaliter em. Zimmermann.  esic B: pro meliori, sicut em. Zimmermann.

Medieval Recollections

Archbishop of Ravenna John XI's letter to Bishop John of Pula issued shortly thereafter -  edited here.

Selected Bibliography
Bernardo Benussi, Nel Medio Evo: Pagine di storia istriana, 2nd ed. (Rovinj–Trieste 2004), pp. 195, 442–43, 511.
Eduard Hlawitska, Franken, Alemannen, Bayern und Burgunder in Oberitalien (774–962): Zum Verständnis der fränkischen Königsherrschaft in Italien (Freiburg 1960), p. 117.
Harald Krahwinkler Friaul im Frühmittelalter. Geschichte einer Region vom Ende des fünften bis zum Ende des 10. Jahrhunderts (Vienna 1992), p. 296.
Editor's Notes

The papal letter shows that the Church of Ravenna continued to own possessions in Istria and in the vicinity of Pula, but it also shows that the region was governed by a count who presided over a March.

Much ink has been spilled over the question of whether Istria formed a separate March during this period or whether it continued to be governed together with Friuli, forming a part of the March of Friuli. Viktor Hasenöhrl, who unfortunately did not know this letter, argued that Istria continued to form a county subjected to the March and the Margraves of Friuli ("Deutschlands südöstliche Marken im 10., 11. und 12. Jahrhunderte", Archiv für österreichische Geschichte 82/2 (1895): pp. 537-39). Benussi (cited above), argued fervently that from Albuin's age onward Istria had become a separate governmental entity, detached from Friuli to form a distinct March of its own. By extension, that would also mean that the next known Margrave governing in Istria, Winther (see the charter edited here), was a margrave of Istria and not of the March of Friuli which included Istria as well. The historiography that ensued largely followed Benussi's local-patriotic interpretation (cf. Hlawitska and Krahwinkler cited above).

However, a different interpretation is at least just as likely, if not even more likely: Albuin was a count who governed the March of Friuli which simply included Istria. Bearing in mind that at this time the terms "comes" and "marchio" were still largely interchangeable, there is really nothing in the way of this interpretation.

How to Cite
First citation: Josip Banic (ed.), Fontes Istrie medievalis, vol. 2: A 804 usque ad 1077, doc. 910_PS, (last access: date).
Subsequent citations: FIM, 2: doc. 910_PS.