Explanation: During the Italian campaign of the Carthaginian general Hannibal Barca, Carthaginian forces ravaged the allies of the Roman Republic up and down the Italian peninsula for some ~15 years. Roman forces hesitated to meet him in open battle, and he largely had his pick of targets.

... but his lack of siege equipment meant that every success against fortified cities came at a high cost in time and supplies. While most siege equipment would have been constructed on site, the lack of a strong engineering corps and the diversity of Hannibal's mercenary army (many of whom did not even share a common language or command structure) meant that coordinating engineering efforts was not always a quick or efficient undertaking.

By contrast, even the relatively early militia-legions of the Roman Republic at this point were organized and trained for manual labor of that sort en masse. The first thing a legionary learns is obedience; the second, labor; and combat only third! Get digging, legionary! So whenever Hannibal would leave a conquered city, the Romans would wait until he was just far enough away to make returning a dangerous prospect, and then swoop in and re-take the city FOR ROME in a fraction of the time.

What a frustrating game of whack-a-mole!