The construction of Johannipolis, by which the history of the classical and early mediæval fortifications of Rome is brought to a close, is described by one document only: an inscription above the gate of the castle, which was copied first by Cola di Rienzo, and later by Pietro Sabino, professor of rhetoric in the Roman archigymnasium (Sapienza), towards the end of the fifteenth century. A few fragments of this remarkable document are still preserved in the cloister of the monastery. It states that Pope John VIII. raised a wall for the defence of the basilica of S. Paul's and the surrounding churches, convents, and hospices, in imitation of that built by Leo IV. for the protection of the Vatican suburb. The determination to fortify the sacred buildings at the second milestone of the Via Ostiensis was taken, as I have just said, in consequence of the inroads of the Saracens, which, under the pontificate of John, had become so frequent. The atrocities which marked their second landing on the Roman coast were so appalling that the whole of Europe was shaken with terror. Having failed in his attempt to secure help from Charles the Bald, John placed himself at the head of such scanty forces as he could gather from land and sea, under the pressure of events. Ships from several harbors in the Mediterranean met in the roads of Ostia; and on hearing that the hostile fleet had sailed from the bay of Naples, the Pope set sail at once. The gallant little squadron confronted the infidels under the cliffs of Cape Circeo, and inflicted upon them such a bloody defeat that the danger was averted, at least for a time. The church galleys came back to the mouth of the Tiber, laden with a considerable booty. It seems that the advance fort of Johannipolis was finished and consecrated by Pope John soon after the naval battle of Cape Circeo (A. D. 877), because the inscription above referred to speaks of him as a _triumphant_ leader,--SEDIS APOSTOLICÆ PAPA JOHANNES OVANS.