The canal of Trajan continued to be kept open, after the building mania, to which it owed its origin, had ceased. It had extended the sphere of the export trade of the Delta; and it continued to serve as the means of transporting the blocks of porphyry--for which there was a constant demand at Rome and Constantinople, and, indeed, in almost every city of wealth in the Roman empire. Eusebius, in his ecclesiastical history, mentions that the porphyry quarries of the Thebaid were worked during the time of the great persecution, in the reign of Dioclesian. He says, "that one hundred martyrs were selected from the innumerable crowd of Christians condemned to labour in the Thebaid, in the place called Porphyritis, from the marble which was quarried at the spot."[1] [1] Eusebius, lib viii. c. 8. In the reign of Justinian, we find these quarries still worked on a considerable scale, as they are alluded to more than once by Paul the Silentiary, in his description of the Church of St Sophia at Constantinople. He affords evidence that the porphyry still continued to be transported by the Nile to Alexandria; and though his words contain no express mention of the canal, it is evident that the workmen of Justinian would always prefer the easier road by Myos Hormos and Arsinoee, to the almost impracticable task of conveying the blocks across the desert.[1] In the reign of Justin I., the trade of the Red Sea was of great importance, and must have created an immense demand for the agricultural produce of Egypt. The King of Ethiopia, resolving to attack Dunaan, the Jewish king of the Homerites in Arabia, collected, during the winter, a fleet of seven hundred Indian vessels, and six hundred trading ships, belonging to the Roman and Persian merchants who visited his kingdom.[2] [1] Pauli Silentianii Descripto Magnae Ecclesiae Sanctae Sophiae, v. 379, 620. [2] Acts of the Martyrs; Metaphrast. Ap. Sur. tom v. p. 1042.