These jealous chieftains, however, had reason to be startled in the spring of 1823, when they heard that eighty thousand Mussulmans were to be sent to attack the Isthmus of Corinth; that forty thousand more were to undertake the siege of Missolonghi; that fifty thousand in addition were to co-operate in Thessaly and Attica; while a grand fleet of one hundred and twenty sail was to sweep the Aegean and reduce the revolted islands. It was, however, the very magnitude of the hostile forces which saved the Greeks from impending ruin; for these forces had to be fed in dried-up and devastated plains, under scorching suns, in the defiles of mountains, where artillery was of no use, and where hardy mountaineers, behind rocks and precipices, could fire upon them unseen and without danger. There was more loss from famine and pestilence than from foes,--a lesson repeatedly taught for three thousand years, but one which governments have ever been slow to learn. Alexander the Great had learned it when he invaded Persia with a small army of veterans, rather than with a mob of undisciplined allies. Huge armies are not to be relied on, except when they form a vast mechanism directed by a master hand, when they are sure of their supplies, and when they operate in a wholesome country, with nothing to fear from malaria or inclemency of weather. Then they can crush all before them like some terrible and irresistible machine; but only then. This the old crusaders learned to their cost, as well as the invading armies of Napoleon amid the snows of Russia, and even the disciplined troops of France and England when they marched to the siege of Sebastopol. Hence, in spite of the divisions of the Greeks, which paralyzed their best efforts, the Turkish armies effected but little, great as were their numbers, in the campaign of 1823. The intrepid Marco Bozzaris, with only five thousand men, kept the Turks at bay in Epirus, and chased a large body of Albanians to the sea; while Odysseus defended the pass of Thermopylae, and prevented the advance of the Turks into Southern Greece. The grand army destined for the invasion of the Morea gradually melted away in attacking fortresses, and under the desultory actions of guerilla bands amidst rocks and thickets. Bozzaris surprised a Turkish army near Missolonghi by a nocturnal attack, and although he himself bravely perished, the attack was successful. The Turks in renewed numbers, however, advanced to the siege of Missolonghi; but they were again repulsed with great slaughter. The naval campaign from which so much was expected by the Sultan also proved a failure. As usual the Greeks resorted to their fire-ships, not being able openly to contend with superior forces, and drove the fleet back again to the Dardanelles. When the sea was clear, they were able to reinforce Missolonghi with three thousand men and a large supply of provisions; for it was foreseen that the siege would be renewed.