Leo 19 was known as the philosopher: Leo Gramm. 224, 225, 243, Georg. Mon. Cont. 805, 806, 829, Ps.-Symeon 638, 640, 676-677, Theoph. Cont. IV 26 (p. 185) (cited below), V 14 (p. 232) (τοῦ τηνικαῦτα ἐπὶ παντοδαπῇ σοφίᾳ πρωτεύοντος), Zon. XVI 4.12. He was related to Ioannes (the iconoclast patriarch Ioannes 5), probably a cousin: Theoph. Cont. IV 26 (p. 185) (cited below), IV 27 (p. 191).

Several stories about him during the reign of Theophilos 5 are preserved in the tradition deriving from Symeon the Logothete. A student of his (Manikophagos 1) supposedly betrayed the city of Amorion to the Arabs in 838: Leo Gramm. 224, Georg. Mon. Cont. 805, Ps.-Symeon 638. Later the student (Manikophagos 1) is said to have told the caliph (al-Ma'mun 1) about his teacher, whereupon the caliph wrote to Leo 19 in Constantinople inviting him to come to see him as an honoured guest; afraid of the consequences, Leo 19 revealed the letter to the emperor Theophilos 5, who in this way learned about Leo 19's reputation for knowledge; the emperor Theophilos 5 established Leo 19 as a teacher (μαθητὴν) in the palace of the Magnaura and made available to him all the resources which he needed; subsequently Leo 19 was made metropolitan bishop of Thessalonike: Leo Gramm. 225, Georg. Mon. Cont. 806, Ps.-Symeon 640. Under Theophilos 5 at the Magnaura palace he was asked by the emperor to interpret an obscure writing found in the palace library; neither he nor the patriarch Ioannes 5 could explain it and eventually it was solved by Methodios 1: Ps.-Symeon 644. Identified as the philosopher Leo 19 who became bishop of Thessalonike (ὁ φιλόσοφος Λέων ὁ Θεσσαλονίκης γενόμενος πρόεδρος), he is credited with devising a system of sending information about events on the frontier with the Arabs near Tarsos, by means of two synchronised clocks and a chain of torches across Asia Minor; the system was abandoned by Michael III (Michael 11), supposedly after a message arrived interrupting the chariot races: Ps.-Symeon 681-682. In view of the evidence of Theophanes Continuatus (see below) it is impossible to accept all of this tradition. It seems unlikely that Theophilos 5 was unaware of Leo 19 and his abilities, when Leo 19 was related to Theophilos 5's own tutor, Ioannes 5. The request from the caliph is probably genuine, though the date is not, since the caliph was al-Ma'mun 1, who died in 833, five years before the capture of Amorion. The stories involving Leo 19 and the Magnaura under Theophilos 5 are probably inventions inspired by his later, better attested, connection with the Magnaura; in all probability Leo 19 was a noted scholar under Theophilos 5 who enjoyed favour as a relative of Ioannes 5 and who was given the post of bishop of Thessalonike during Ioannes 5's patriarchate; he was perhaps an iconoclast, but in any event his relationship with Ioannes 5 probably cost him his see when iconoclasm was overthrown (see further below).

Leo 19's story is also narrated in Theophanes Continuatus IV 27-29. The same account of how he came to the notice of the emperor Theophilos 5 is told as in the tradition from Symeon the Logothete but with additions. Leo 19 is said to have had the leisure, the ability and the zeal to pursue his studies of philosophy and its sister subjects, arithmetic, geometry, astronomy and music (τῆς φιλοσοφίας καὶ τῶν αὐτῆς ἀδελφῶν, ἀριθμητικῆς τέ φημι καὶ γεωμετρίας καὶ ἀστρονομίας, ἀλλὰ καὶ τῆς πολυθρυλήτου μουσικῆς), to the most advanced level, surpassing all others in each; he then took pupils and taught them whichever subject they preferred, though he could only afford to live in a poor and humble dwelling place: Theoph. Cont. IV 27 (pp. 185-186). He once told a friend that he mastered grammar and poetry while living in Constantinople, but learned rhetoric, philosophy and arithmetic on the island of Andros; he encountered a learned man there (Anonymus 221) who trained him in the principles of these; then, when he sought deeper knowledge than this man could give him, he visited various monasteries scattered around the island and acquired and studied books that were kept in them; he withdrew to the high parts of the mountains to develop his knowledge and when he could advance no further he returned to Constantinople and began to teach: Theoph. Cont. IV 29 (p. 192). One of his former pupils (Manikophagos 1), trained by him in geometry, was captured by the Arabs and so impressed the caliph al-Ma'mun 1 (died 833) with his understanding of the subject that the caliph enquired about his teacher; hearing that Leo 19 lived in poverty and obscurity, the caliph sent the pupil with a letter inviting Leo 19 to come and live among the Arabs and share his knowledge, promising him all honour and riches; on receiving the letter Leo 19 was alarmed and hastened to disclose his pupil's story and the contents of the letter to a high official, the logothetes Theoktistos 3 and in this way he came to the attention for the first time of the emperor himself; Theophilos 5 summoned him to court, made him rich and urged him to teach publicly, in the Church of the Forty Martyrs: Theoph. Cont. IV 27 (pp. 186-189), cf. Zon. XVI 4. 12-24 (a similar story). Soon afterwards the caliph, realising that Leo 19 was not coming to the Arabs, wrote him a letter containing various geometrical and astrological problems and other knotty subjects, all of which Leo 19 resolved for him and in his reply he also added information about signs predicting the future, to impress the caliph; al-Ma'mun 1 then wrote directly to Theophilos 5 asking for Leo 19 to be sent to him for a short while to teach what he knew and offering to pay large sums of gold and to make an eternal peace; Theophilos 5 refused and, to show greater honour to Leo 19, instructed his kinsman Ioannes 5 the patriarch to appoint him metropolitan bishop of Thessalonike, as his relative and a man of great learning (ὡς πλήρη σοφίας ὄντα καὶ ὡς οἰκειούμενον τούτῳ κατὰ συγγένειαν): Theoph. Cont. IV 27 (pp. 189-191). He was instructed to teach by Theophilos 5 and then was made archbishop of Thessalonike by him: Zon. XVI 4. 24. He was highly esteemed in Thessalonike, not least because when the harvest failed once he gave advice on when to sow, based on astrological signs, and the result was a bumper harvest: Theoph. Cont. IV 28 (p. 191).

Leo 19 was for a time bishop of Thessalonike (see above); he was deposed from this post (perhaps in 843, after the dismissal of Ioannes 5 and the overthrow of iconoclasm) and subsequently was appointed as head of the new school of secular studies founded at Constantinople in the Magnaura palace by the Kaisar Bardas 5; he also taught philosophy in the school: Theoph. Cont. IV 26 (p. 185) (ἦρχε δὲ καὶ τῆς τοιαύτης σχολῆς τὴν μὲν φιλοσοφίαν ἐξηγούμενος Λέων ἐκεῖνος ὁ μέγας τε καὶ φιλόσοφος, ὃς κατὰ συγγένειαν μὲν τοῦ ἐξαδέλφου τῷ πατριάρχῃ Ἰαννῇ ᾠκείωτο, τὸν θρόνον δὲ τῆς Θεσσαλονίκης κατέχων, ἐπειδὴ νῦν ἐκ καθαιρέσεως ἐσχόλαζεν, εἰς ταύτην προεβιβάζετο τὴν σχολήν, τὴν ἀμαθίαν πόρρω ποι ἀπελαύνων καὶ ἀποτρεπόμενος). He was dismissed from his see for refusing to venerate icons and was subsequently given authority over the other teachers by Bardas 5 in the latter's new school: Zon. XVI 4. 25-26. He was bishop of Thessalonike for three years; he was then deposed and resumed teaching, becoming head of the school of philosophy at the Magnaura; one of his pupils, Theodoros 162, was head of the school of geometry, Theodegios 1 was in charge of that of astronomy and Kometas 4 of Greek grammar; resources and encouragement came from Bardas 5 and great progress was made in the advancement of learning: Theoph. Cont. IV 29 (p. 192) (καὶ νῦν δὲ ἐπεὶ μετὰ τρεῖς χρόνους (τοσοῦτος δὲ ὁ τῆς τοῦ θρόνου ἀντιλήψεως χρόνος) ἐκ τῆς καθαιρέσεως αὖθις ἐσχόλαζεν, τῆς κατὰ τὴν Μαγναύραν μὲν οὗτος ἦρχε φιλοσόφου σχολῆς). The chronology given suggests that he was deposed in 843 and so presumably he became bishop of Thessalonike in 840; this is inconsistent with the alleged role of the letter from the caliph Mamoun (al-Ma'mun 1) in prompting Theophilos 5 to make him bishop, but, that apart, the story fits into a reasonable chronology if Leo 19 came to Theophilos 5's notice in or before 833 and acquired imperial patronage then but did not become bishop of Thessalonike until 840, after his kinsman Ioannes 5 had become patriarch of Constantinople. See also above. This account is in some contradiction with the other sources derived from Symeon the Logothete (see above). Evidently events in the reign of Theophilos 5 have been transferred to that of Michael III (Michael 11), or vice versa. His connection with Bardas 5 suggests that he became teacher in the Magnaura under Michael III (Michael 11), and so that he was bishop of Thessalonike first (presumably under Theophilos 5 and around the time when Ioannes 5 was patriarch of Constantinople) and some time thereafter became head of the school. A philosopher, he was appointed by Bardas 5 to teach philosophy at the Magnaura and was rewarded out of imperial funds; his pupil Theodoros 162 taught geometry: Genesius IV 17 (Λέοντα τὸν πάνυ φιλόσοφον κατὰ τὴν φιλοσοφίαν ... διδάσκαλον). In 866 he warned the Kaisar Bardas (Bardas 5) against Basilios 7 (the future emperor Basil I) and advised him against going on the planned expedition to Crete, since he would never return from it: Leo Gramm. 243, Georg. Mon. Cont. 829, Ps.-Symeon 676-677, cf. Theoph. Cont. V 14 (p. 232) (he foretold the overthrow of the imperial family by a young man and then, when Basilios 7 came to prominence, identified him to Bardas 5 as the man). On one occasion when statues near to the Church of St Anna in the Second District of Constantinople were overthrown from their firm foundations by an earthquake he described the event as foretelling the downfall of the person who was second to the emperor himself: Theoph. Cont. IV 34 (p. 197) (styled (ὁ μαθηματικὸς Λέων). He predicted the fall of Bardas 5 when a statue called The Second (τὸ δεύτερον) fell in an earthquake and foretold that his successor would be Basilios 7: Genesius IV 22.

(Publishable link for this person: )