Phocas (also called Foca and Focas, the manuscripts and references alternating between these forms) is identified as grammaticus urbis Romae by the manuscript Par. Lat. 8093.  He was active between the 4^th and 5^th c. AD: it is certain that he precedes Priscian, who cites his grammatical treatise (GL II 515.16), and that he works after Donatus, since his Vita Vergilii depends on Aelius Donatus’ biography of the poet (middle of the 4^th c.).  Two separate arguments have been proposed that hypothesize a earlier dating: first, the inclusion of Phocas in a list of auctores temporum superiorum found in Cassiodorus (GL VII 214, 23-26); second, the possibility that Phocas did not use Donatus’ Vita Vergilii, but the source of that text, i.e. Suetonius’ biography of the poet.  The first argument, which Mazhuga recently introduced to date Phocas to the first half of the 3^rd c. AD, is invalidated by the poor reliability of Cassiodorus’ chronological references.  Access to Suetonius, on the other hand, which was the basis for Strzelecki’s dating to the start of the 4^th c. AD , does not on its own support the notion that Phocas anteceded Donatus: Schmidt, who had previously argued for this dating, subsequently placed Phocas at the start of the 5^th c. AD even as he reiterated the author’s dependence on Suetonius.  Kaster has also accepted a dating after Donatus and demonstrated alternative criteria to support it: the author’s (probably) Christian outlook, identifiable e.g. in the prose preface to the De nomine et verbo, where he speaks of his teaching as a gymnasium sapientiae, quo ad beatam vitam semita demonstratur (5.411.6-7); echoes of Charisius and Diomedes that Keil identified in the De nomine et verbo; and the frequency with which he cites Lucan and Juvenal, authors introduced rather late into the scholastic canon.  The Vita Vergilii is the only Vergilian biography that has come down to us in verse.  It is attested by a single codex (Par. Lat. 8093) and remained unknown until the 16^th c.  In contrast, the De nomine et verbo, a grammatical treatise preceded by a verse preface, enjoyed a wide diffusion in the course of the Middle Ages (it is attested by more than 80 manuscripts and cited by numerous authors).  The treatise depends on sources that were also utilized by Charisius and Priscian.  It discusses the genders and declensions of nouns, the conjugations of verbs, and irregular forms.  Two other short grammatical treatises, the De aspiratione and De orthographia, were probably also attributed to Phocas during the medieval period.  [F. Stok; tr. C. L. Caterine].