The Spartans had for some time been anxious to open hostilities; an act of Athenian aggression gave them an opportunity. Meanwhile in Sicily Lamachus had perished in attacking a Syracusan cross-wall. Left in sole command, Nicias remained inactive, while Gylippus, despatched from Sparta, arrived in Syracuse just in time to prevent it from capitulating. The seventh book is the record of continued Athenian disasters. Little by little Gylippus developed the Syracusan resources. First he made it impossible for the Athenians to circumvallate the city; then he captured the naval stores of the enemy, forcing them to encamp in unhealthy ground. Nicias had begged the home government to relieve him of command owing to illness. Believing in the lucky star of the man who had taken Nissea they retained him, sending out a second great fleet under Demosthenes. The latter at once saw the key to the whole situation. The Syracusan cross-wall which Nicias had failed to render impassable must be captured at all costs. A night attack nearly succeeded, but ended in total defeat. Demosthenes immediately advised retreat; but Nicias obstinately refused to leave. In the meantime the Syracusans closed the mouth of their harbour with a strong boom, penning up the Athenian fleet. The famous story of the attempt to destroy it calls out all the author's powers of description. He draws attention to the narrow space in which the action was fought. As long as the Athenians could operate in open water they were invincible; but the Syracusans not only forced them to fight in a confined harbour, they strengthened the prows of their vessels, enabling them to smash the thinner Athenian craft in a direct charge. The whole Athenian army went down to the edge of the water to watch the engagement which was to settle their fate. Their excitement was pitiable, for they swayed to and fro in mental agony, calling to their friends to break the boom and save them. After a brave struggle, the invaders were routed and driven to the land by the victorious Syracusans.