He accompanied this emperor, for whom he expresses enthusiastic admiration, in his campaigns against the Alamanni and the Persians; after his death he took part in the retreat of Jovian as far as Antioch, where he was residing when the conspiracy of Theodorus (371) was discovered and cruelly put down.
His work was continued in the 5th century by Philostorgius, Socrates, Sozomen and Theodoret, and in later centuries by Theodorus Lector, Evagrius, Theophanes and others.
Bessarion, Theodorus Gaza, Georgius Trepezuntius, Argyropulus, Chal condyles, all had reached Italy before 1453.
According to Suidas and Strabo, he was the author of TEXvac pfT0pucai (rhetorical manuals) and of other works, which should perhaps be attributed to his younger namesake, surnamed Carion, the pupil of Theodorus of Gadara.
The great and splendidly illustrated collections of voyages and travels of Theodorus de Bry and Hulsius served a similar useful purpose on the continent of Europe.
It survived, with various dismemberments, until 1430, when the last prince, Centurione Zaccaria, ceded the remnant of it to his son-in-law, Theodorus II., despot of Mistra.
Of the two chief methods of working bronze, gold and silver, it is probable that the hammer process was first practised, at least for statues, among the Greeks, who themselves attributed the invention of the art of hollow casting to Theodorus and Rhoecus, both Samian sculptors, about the middle of the 6th century B.C. Pausanias specially mentions that one of the oldest statues he had ever seen was a large figure of Zeus in Sparta, made of hammered bronze plates riveted together.
His speeches and letters consist partly of declamations on the usual sophistical themes, partly deal with contemporary historical events: an argument between the fathers of Cynegirus and Callimachus (two Athenians who fell at Marathon) as to which had the better claim to have the funeral oration pronounced over him first; a discussion on the duties of; a king and of his subjects; a defence of the Byzantine general Chandrenos addressed to the emperor; a letter on the cruelties of the Catalans and Turks in Thessaly and Macedonia; a congratulatory letter to Theodorus Metochita; a panegyric on the king of Cyprus.
He was associated with Marsilius Ficinus, Angelus Politianus, and Theodorus Gaza, in the revival of letters in the western world.
A further revision of this code is stated to have been made by Constantine Porphyrogenitus, the son and successor of Leo, but this statement rests only on the authority of Theodorus Balsamon, a very learned canonist of the 12th century, who, in his preface to the Nomocanon of Patriarch Photius, cites passages from the Basilica which differ from the text of the code as revised by the emperor Leo.