Το πλέον σημαντικό και ενδιαφέρον από τα έργα που συνέγραψε ο λόγιος πατριάρχης είναι η «Βιβλιοθήκη», συλλογή περιλήψεων-σημειώσεων από βιβλία του εθνικού και χριστιανικού παρελθόντος. Οι περιλήψεις αυτές φέρονται να γράφτηκαν για έναν και μόνο αποδέκτη σε κλίμα συγκινησιακά φορτισμένο. Προσφέρονται στον Ταράσιο, τον αγαπημένο αδελφό του Φωτίου, ως χαριστήριο ενθύμιο λίγο πριν από το διπλωματικό ταξίδι του συγγραφέα στους Ασσυρίους. Αυτά τονίζονται στην επιστολή που παρατίθεται εισαγωγικά στο έργο και επαναλαμβάνονται σε έναν βαθμό στις καταληκτικές γραμμές, που πάλι απευθύνονται στο ίδιο πρόσωπο. Ό,τι παρεμβάλλεται είναι σημειώματα βιβλιογραφίας, βιβλιοκριτικής, βιογραφίας ή ανθολόγησης κειμένων. Παρά τον εσωστρεφή και προσωπικό της χαρακτήρα, η «Βιβλιοθήκη», όπως φαίνεται, γνώρισε ευρεία διάδοση. Αυτό τουλάχιστον δείχνει ο αριθμός των 25 χειρογράφων στα οποία έχει διασωθεί μέχρι τις μέρες μας. Στον αριθμό αυτόν μπορούν να προστεθούν και εκείνα που περικλείουν μόνο αποσπάσματα από το εκτενές αυτό έργο. Δύο, ωστόσο, χειρόγραφα που σήμερα απόκεινται στη Μαρκιανή Βιβλιοθήκη της Βενετίας, ο «Marcianus graecus 450» του Ι' και ο «Marcianus graecus 451» του ΙΒ' αιώνα, θεωρήθηκαν από τη σχετική φιλολογική έρευνα ως τα βασικά και κύρια τεκμήρια για την κριτική αποκατάσταση του κειμένου. [...]
Photios I (/ˈfoʊʃəs/; Greek: Φώτιος, Phōtios; c. 810 – c. 893a[›]), also spelled Photius or Fotios, was the Ecumenical Patriarch of Constantinople from 858 to 867 and from 877 to 886. He is recognized in the Eastern Orthodox churches as St. Photios the Great.
Photios is widely regarded as the most powerful and influential Patriarch of Constantinople since John Chrysostom, and as the most important intellectual of his time, "the leading light of the ninth-century renaissance". He was a central figure in both the conversion of the Slavs to Christianity and the Photian schism.
Photios was a well-educated man from a noble Constantinopolitan family. Photius's great uncle was the previous Patriarch of Constantinople, Tarasius. He intended to be a monk, but chose to be a scholar and statesman instead. In 858, Emperor Michael III (r. 842–867) deposed Patriarch Ignatius of Constantinople, and Photios, still a layman, was appointed in his place. Amid power struggles between the pope and the Byzantine emperor, Ignatius was reinstated. Photios resumed the position when Ignatius died (877), by order of the Byzantine emperor. The new pope, John VIII, approved Photios's reinstatement. Catholics regard a Fourth Council of Constantinople (Roman Catholic) as anathematizing Photios as legitimate. Eastern Orthodox regard a second council named the Fourth Council of Constantinople (Eastern Orthodox), reversing the first, as legitimate. The contested Ecumenical Councils mark the end of unity represented by the first seven Ecumenical Councils.
S-a păstrat de la patriarhul bizantin Photios o carte care valorează cît o bibliotecă. De altfel, lucrarea lui Photios (de pe la 845-855) a fost numită de comentatori chiar „Bibliotheca”. În limba greacă e „Bibliotheke” sau „Myriobiblon”. Ce este, în fond, această „Bibliotheca”?
E vorba de un catalog nesistematic de cărţi greu de procurat (chiar) în vremea patriarhului. Astăzi multe din cărţile recenzate nu mai există în versiunea în care au fost consultate de Photios. Sau nu mai există deloc. Timpul şi soarta le-au distrus.
Photios consemnează patru romane antice şi medievale. Unul dintre ele se referă, de exemplu, la Ultima Thule -insula fabuloasă de la capătul lumii. Alte recenzii sînt la cărţi de teologie, de istorie (greacă, romană şi bizantină), de filosofie ori de lexicografie. Cîţiva „codici” (aşa au fost numite capitolele lucrării) rezumă oratori, specialişti în arta agriculturii, fabulatori.
În acest sens, patriarhul prezintă cartea despre India a lui Ktesias, în care găsim povestirile cele mai ciudate şi mai pasionante. Ktesias spune (şi patriarhul reţine fără multe întrebări) că în India sînt izvoare fermecate, de unde ţîşneşte ambră (sau miere), că într-o regiune anumită trăiesc pigmeii nu mai înalţi de un cot şi jumătate şi care se înveşmîntează în părul propriu, că munţi plini cu filoane de aur curat sînt păziţi de grifoni etc. etc.
Unele rezumate din „Bibliotheca” conţin extrase. Cîteva (nu foarte multe) oferă doar numele autorului, titlul lucrării şi cîteva observaţii despre stil. În sfîrşit, altele sînt foarte lungi, precum e şi conspectul la cartea lui Ktesias.
Din cîte știu, lucrarea lui Photios există în traducere integrală doar în franceză. Ediţia a fost realizată de savantul René Henry...