For some within the town had undertaken to betray it into his hands, and, by agreement, were to give him a signal by a lighted torch about midnight. But one of the conspirators beginning to repent himself of the design, the rest, for fear of being discovered, were driven to give the signal before the appointed hour. Alcibiades, as soon as he saw the torch lifted up in the air, though his army was not in readiness to march, ran instantly towards the walls, taking with him about thirty men only, and commanding the rest of the army to follow him with all possible speed. When he came hither, he found the gate opened for him and entered with his thirty men, and about twenty more light-armed men, who were come up to them. They were no sooner in the city, but he perceived the Selymbrians all armed, coming down upon him; so that there was no hope of escaping if he stayed to receive them; and, on the other hand, having been always successful till that day, wherever he commanded, he could not endure to be defeated and fly. So, requiring silence by sound of a trumpet, he commanded one of his men to make proclamation that the Selymbrians should not take arms against the Athenians. This cooled such of the inhabitants as were fiercest for the fight, for they supposed that all their enemies were within the walls, and it raised the hopes of others who were disposed to an accommodation. Whilst they were parleying, and propositions making on one side and the other, Alcibiades's whole army came up to the town. And now, conjecturing rightly that the Selymbrians were well inclined to peace, and fearing lest the city might be sacked by the Thracians, who came in great numbers to his army to serve as volunteers, out of kindness for him, he commanded them all to retreat without the walls. And upon the submission of the Selymbrians, he saved them from being pillaged, only taking of them a sum of money, and, after placing an Athenian garrison in the town, departed.
During this action, the Athenian captains who besieged Chalcedon concluded a treaty with Pharnabazus upon these articles: That he should give them a sum of money; that the Chalcedonians should return to the subjection of Athens, and that the Athenians should make no inroad into the province whereof Pharnabazus was governor; and Pharnabazus was also to provide safe conducts for the Athenian ambassadors to the King of Persia. Afterwards, when Alcibiades returned thither, Pharnabazus required that he also should be sworn to the treaty; but he refused it, unless Pharnabazus would swear at the same time. When the treaty was sworn to on both sides, Alcibiades went against the Byzantines, who had revolted from the Athenians, and drew a line of circumvallation about the city. But Anaxilaus and Lycurgus, together with some others, having undertaken to betray the city to him upon his engagement to preserve the lives and property of the inhabitants, he caused a report to be spread abroad, as if by reason of some unexpected movement in Ionia, he should be obliged to raise the siege. And, accordingly, that day he made a show to depart with his whole fleet; but returned the same night, and went ashore with all his men at arms, and, silently and undiscovered, marched up to the walls. At the same time, his ships rowed into the harbour with all possible violence coming on with much fury, and with great shouts and outcries. The Byzantines, thus surprised and astonished, while they all hurried to the defence of their port and shipping, gave opportunity to those who favoured the Athenians securely to receive Alcibiades into the city. Yet the enterprise was not accomplished without fighting, for the Peloponnesians, Boeotians, and Megarians, not only repulsed those who came out of the ships, and forced them on board again, but, hearing that the Athenians were entered on the other side, drew up in order, and went to meet them. Alcibiades, however, gained the victory after some sharp fighting, in which he himself had the command of the right wing, and Theramenes of the left, and took about three hundred, who survived of the enemy, prisoners of war. After the battle, not one of the Byzantines was slain, or driven out of the city, according to the terms upon which the city was put into his hands, that they should receive no prejudice in life or property. And thus Anaxilaus, being afterwards accused at Lacedaemon for this treason, neither disowned nor professed to be ashamed of the action; for he urged that he was not a Lacedaemonian, but a Byzantine, and saw not Sparta but Byzantium, in extreme danger; the city so blockaded that it was not possible to bring in any new provisions, and the Peloponnesians and Boeotians, who were in garrison, devouring the old stores, whilst the Byzantines, with their wives and children, were starving, that he had not therefore, betrayed his country to enemies, but had delivered it from the calamities of war, and had but followed the example of the most worthy Lacedaemonians, who esteemed nothing to be honourable and just, but what was profitable for their country. The Lacedaemonians, upon hearing his defence, respected it, and discharged all that were accused.