While Claudius thought, that if he were able with his fleet to give security to the Athenians it was as much as could be expected at present, a fortunate opportunity was thrown in his way of accomplishing a much more important enterprise.
23.

Some exiles driven from Chalcis, by ill treatment received from the king's party, brought intelligence, that the place might be taken without even a contest; for that both the Macedonians, being under no immediate apprehension from an enemy, were straying idly about the country; and that the townsmen, depending on the Macedonian garrison, neglected the guard of the city.

Claudius, on this authority, set out and though he arrived at Sunium early enough to have sailed forward to the entrance of the strait of Euboea, yet fearing that, on doubling the promontory, he might be descried by the enemy, he lay by with the fleet until night.

As soon as it grew dark he began to move, and, favoured by a calm, arrived at Chalcis a little before day; and then, approaching the city, on a side where it was thinly inhabited, with a small party of soldiers, and by means of scaling ladders, he got possession of the nearest tower, and the wall on each side; the guards being asleep in some places, and in others no one being on the watch.
Thence they advanced to the more populous parts of the town, and having slain the sentinels, and broke open a gate, they gave an entrance to the main body of the troops.

These immediately spread themselves throughout the whole city, and increased the tumult by setting fire to the buildings round the forum, by which means both the granaries belonging to the king, and his armoury, with a vast store of machines and engines, were reduced to ashes.