Pope John IV dispatches abbot Martin to journey across Dalmatia and Istria to ransom the captives (imprisoned, one would assume, by the still pagan Slavs) and return the relics of the saints from these endangered places to Rome; narrative account from the Book of the Popes (Liber pontificalis).
LXXIIII.a Iohannes, natione Dalmata, ex petreb Venantio scolastico, sedit annum I, menses VIIII, dies XVIIII.1 Hic temporibus suis misit per omnem Dalmatiam seu Istriamc multas peccunias per sanctissimum et fidelissimum Martinum abbatem propter redemptionem captivorum qui captid erant a gentibus. Eoe tempore fecit ecclesiam beatis martiribus Venantio, Anastasio, Mauro et aliis multis martiribusf quorum reliquias de Dalmatiag et de Istriah adduci preceperat, et recondiditi eas in ęcclesia suprascripta, iuxta fontem Lateranensem, iuxta oratorium beati Iohannis evangelistę, hanc itaque ęcclesiam ornavitj et diversa dona ibik optulit.
a) ex LIIII corr. B. b) sic B: pro patre. c) Histriam ed. Duchesne. d) depraedati ed. Duchesne. e) eodem ed. Duchesne. f) aliis multis martiribus] aliorum multorum martyrum ed. Duchesne. g) ex Dalmaticus corr. B. h) Dalmatia et de Istria] Dalmatias et Histrias ed. Duchesne. i) sic B; recondit ed. Duschesne. j) hanc itaque ęcclesiam ornavit] quam ornavit ed. Duchesne. k) om. ed. Duchesne.
1) 24th of December, 640 – 12th of October, 642.
74. John, born in Dalmatia, son of the scholar Venantius, held the see 1 year 9 months 18 days. In his time, he sent much money by the most holy and trustworthy abbot Martin throughout Dalmatia and Istria to redeem captives who had been captured by the barbarians. He built a church for the sainted martyrs Venantius, Anastasius, Maurus, and many other martyrs whose relics he had ordered to be brought from Dalmatia and Istria; he deposited them in that church close to the Lateran Font and the oratory of St John the Evangelist.
[the translation, slightly modified by the editor, is based on Raymond Davis (trans.), The Book of Pontiffs (Liber pontificalis): The Ancient Biographies of First Ninety Roman Bishops to AD 715, 3rd ed., Translated Texts for Historians 6 (Liverpool 2010), pp. 64–65]
"Eodem tempore Iohannes summus pontifex apostolice sedis, cum esset Dalmatinus natione, audiens sue gentis miserabilem casum valde condoluit missitque abbatem quendam, Martinum nomine, cum multa pecunie quantitate pro redimendis captivis. Qui veniens ad partes Dalmatie multos redemit captivos de Sclavis eosque ad parentes suos remisit. Iste Martinus ex apostolica iussione multorum sanctorum reliquias accepit in partibus Dalmatie et Ystrie et detulit eas Romam ad predictum papam Iohannem. Qui venerabilis pontifex eas reverenter suscipiens recondidit apud ecclesiam beati Iohannis Lateranensis, ubi est fons baptisterii et ibidem iuxta fecit depingi ymaginem beati Domnii cum pallio et ceteris pontificalibus indumentis totum ex musio aureo. Similiter fecit ymaginem beati Anastasii inter alios sanctos." – Thomas Archidiaconus, Historia Salonitana, cap. 8/3, ed. Olga Perić–Mirjana Matijević Sokol, (Split 2003), p. 38.
The episode narrated in the Liber pontificalis forms part of the story-arc of early medieval Slavic migrations into Istria, a process that began in the late 6th century (see this document).
It is traditionally argued that the relics of St. Maurus explicitly mentioned in the passage were taken from Poreč, a civitas (in the medieval sense of the word, that is, a seat of a Bishopric) whose patron saint has indeed been St. Maurus. Both Poreč and Split (whose patron saint has been St. Domnius, also explicitly mentioned in the hereby edited passage) continued to possess the relics of their patron saints deep into the late medieval centuries (Poreč lost its relics in 1354 during a Genoese incursion); thus, it is argued (Stanko Škunca, referenced above, p. 193), that abbot Martin only retrieved parts of the relics.
Be that as it may, from the mid-7th century onwards there are no more written primary sources attesting to violent Slavic incursions into Istria: the next document explicitly mentioning Slavic presence in Istria is the Plea of Rižana (Placitum Rizianense) - edited here.
The images from the Vatican library are available for consultation online, but the library's copyrights prevent the posting of these images on other web pages. The users are thus directed to this page.