Phalanxes facing the legion were vulnerable to the more flexible Roman "checkerboard" deployment, which provided each fighting man a good chunk of personal space to engage in close order fighting. The manipular system also allowed entire Roman sub-units to manoeuvre more widely, freed from the need to always remain tightly packed in rigid formation. The deep three-line deployment of the Romans allowed combat pressure to be steadily applied forward. Most phalanxes favoured one huge line several ranks deep. This might do well in the initial stages, but as the battle entangled more and more men, the stacked Roman formation allowed fresh pressure to be imposed over a more extended time. As combat lengthened and the battlefield compressed, the phalanx might thus become exhausted or rendered immobile, while the Romans still had enough left to not only manoeuvre but to make the final surges forward. Hannibal's deployment at Zama appears to recognize this—hence the Carthaginian also used a deep three-layer approach, sacrificing his first two lower quality lines and holding back his combat-hardened veterans of Italy for the final encounter. Hannibal's arrangement had much to recommend it given his weakness in cavalry and infantry, but he made no provision for one line relieving the other as the Romans did. Each line fought its own lonely battle and the last ultimately perished when the Romans reorganized for a final surge.