ISIDORO of CHIOS, saint, martyr. — A soldier belonging to the fleet of Alexandria at the time of the emperor Decius, holding the rank of assistant (optio) for the distribution of rations. Shortly after his ship had put in at the island of Chios, he was denounced as a Christian by the centurion Julius and put to death by the sword by the military prefect Numerian. So states the *Passio*, which is not an authentic document (BHL, 4478-80; Supplementum, p. 179; BHG, 960-61, cf. also Anal. Boll., 32 [1913], p. 468; 54 [1936], p. 396).
It is not excluded that he may have been a victim of Diocletian rather than of Decius. In any case, the cult of St ISIDORO of Chios, owing to the renown of his shrine, which was known even in the West (cf. Gregory of Tours, *In gloria Martyrum*, 101), has overshadowed his namesakes among the martyrs, such as the one mentioned by Eusebius of Caesarea, also an Egyptian, a victim of the persecution of Decius (*Hist. eccl.*, VI, 41, 19). It is therefore highly probable that references to relics or churches of St ISIDORO, without further specification, down to the early Middle Ages, should be understood as referring to our martyr. Thus, in Constantinople, the chapel containing the relics of St ISIDORO, built next to St Irene by St Marcian (5th century); in Calama (Guelma) and Henchir Djulta in Africa, inscriptions mentioning the relics of St ISIDORO; the lamp bearing the name of St ISIDORO found in Egypt and the church dedicated to him at Deir el-Medinet; in Rome, the church and monastery mentioned respectively in the *Einsiedeln Topography* (ed. R. Valentini-G. Zucchetti, *Codice topografico della città di Roma*, II, Rome 1942, p. 187) and in the *Liber Pontificalis* in the biography of Leo III (II, p. 24; Valentini-Zucchetti, *op. cit.*, p. 301). The relics of St ISIDORO, transferred to Venice in 1125 (cf. *Translatio di Cerbano Cerbani*: BHL, 481), were later placed by Doge Andrea Dandolo in St Mark’s, in the sumptuous chapel which he had decorated with scenes from the saint’s life (1354-55).
The *Synaxarium Constantinopolitanum* (*Synax. Constantinop.*, col. 683) and the Berne manuscript of the *Martyrologium Hieronymianum* (*Martyr. Hieronymus*, pp. 253, 255) commemorate him on 14 May; the *Roman Martyrology* (*Martyr. Romanum*, pp. 50, 190) on 5 February and 15 May, treating him as two distinct persons, whereas both notices refer to the same individual. — See pl. XVIII.
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**ISIDORO the GNOSTIC.** — Son and disciple of Basilides.
**He wrote the following works:** *On the Soul that has grown* (Περὶ τῆς προσοδίας ψυχῆς; cf. Clement of Alexandria, *Strom.*, II, 20, 113); *Ethics* (Ἠθικά, ibid., III, 1, 2); *Signs of the Prophet Parchor* (Σημεῖα τοῦ προφήτου Παρχόρ, ibid., VI, 6, 53). ISIDORO distinguished between the rational soul and the animal soul, which had grown through the transmigration of souls in the world of stones, plants and animals. The rational soul must dominate the lower soul. ISIDORO based himself on traditions of Matthias (Clement of Alexandria, VII, 108; Hippolytus, *Ref.*, VII, 20) and on the authority of the prophets Barba and Barkoph (identical with Parchor; V. Agrippa Castro in Eusebius, *Hist. eccl.*, IV, 7, 7). Epiphanius (*Haer.*, 32, 3) knows a work, *Parenetic of ISIDORO*, which may be identical with his *Ethics*. Strange is the prophecy of Cham, which ISIDORO cites and which would have been the source of the philosophy of Pherecydes (Clement of Alexandria, *Strom.*, VI 6, 53), just as Parchor would have been the source of the philosophy of Aristotle. This may perhaps be an expression of Egyptian nationalism asserting the dependence of Greek philosophy on supposed Egyptian authors (for other manifestations of Egyptian nationalism V. recently G. Bardy, in *Revue d'histoire ecclés.*, 45 [1950], p. 5 sq.).
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**ISIDORO the MERCATOR:** V. *PSEUDO-ISIDORO*.