Governor Henriquez began the circumvallation of the city in 1630, and his successor, Sarmiento, concluded it between the years 1635 and 1641.

Fearing no longer any attack from without, he set resolutely to work to continue his circumvallation.

Could Demosthenes succeed in storming this outwork, and in reëstablishing the Athenian troops on the high ground, he might fairly hope to be able to resume the circumvallation of the city and become the conqueror of Syracuse; for when once the besiegers' lines were completed, the number of the troops with which Gylippus had garrisoned the place would only tend to exhaust the stores of provisions and accelerate its downfall.