History of the Peloponnesian War

On the next day some of the Athenians proceeded to build the wall to the north of the round fort, while others brought together stones and wood and began to lay these down along the line towards the place called Trogilus, in which direction the line of circumvallation would be shortest from the Great Harbour to the outer sea.

But the Syracusans, at the suggestion of their generals, and especially of Hermocrates, were no longer inclined to risk pitched battles with their whole force against the Athenians. It seemed better to build a wall across the line where the Athenians were going to bring their wall, so that if they got ahead of them the Athenians would be blocked off, and they decided at the same time, if the Athenians should attack them while at this work, to send a part of the army against them;

and they expected that they would get ahead of the Athenians in occupying the approaches with their stockades, and that they would cease from their work and all turn against them. Accordingly they went out and proceeded to build, starting from the city and carrying a cross-wall below the round fort of the Athenians, chopping down the olive-trees of the precinct and setting up wooden towers.

The Athenian ships had not yet sailed round from Thapsus into the Great Harbour, but the Syracusans were still masters of the parts about the sea, and the Athenians brought their supplies from Thapsus by land.