At this stage Venice once more intervenes, taking up the cause of Verona against the tyrant of Padua, whom, having defeated him by her carefully-chosen and supervised mercenaries, she put to death (1406). He had been the ally of Florence; but Florence let him fall, being now wholly bent on reconquering Pisa, her natural seaport. Pisa, in turn, always invincibly opposed to Florentine rule, was on commercial grounds backed by Genoa, now under the nominal rule of a representative of the King of France, who, however, sought to sell Pisa to the Florentines, and did receive from them 200,000 florins. Still resisting, the Pisans recalled an exile to lead them; and he in turn sold them for 50,000 florins, this time to their complete undoing. Refusing all Florentine favours, the bulk of the ruling middle-class abandoned the city for ever, taking much of its special commerce with them. Meantime, the kingdom of Naples, under an energetic king, Ladislaus, had acquired most of the States of the distracted Church, menaced Florence, and was pressing her hard, despite French support, when Ladislaus died (1414). By this time the new Visconti was establishing himself at Milan by means of mercenaries, commanded for him by well-chosen captains. Six times were the Florentines defeated by his forces; till his capable general, Carmagnola, whom he had disgraced, revealed to the Council of Venice his master's intention to attack them; and Venice joined Florence to crush the tyrant. Carmagnola, acting slackly, met ill success, and was therefore executed by his Venetian masters. But the Visconti too finally died defeated, leaving his power to a new adventurer, Francesco Sforza, who had married his daughter, and had fought both for and against him in the endless imbroglio of Italian conspiracy. Florentine republicanism was now near its euthanasia. By the fatal law of empire, the perpetual enterprise of destroying other men's freedom left Florence unfit to use or to defend her own; and the tyrants of Pisa became meet for the yoke of tyranny. The family of Medici, growing rapidly rich, began to use the power of capital as elsewhere less astute adventurers used the power of the sword. From the overthrow of the _ciompi_ party in 1382 to 1434, the Republic had been ruled by a faction of the new commercial aristocracy with substantial unity; and the period is claimed as the most prosperous, intellectually and materially, though not the most progressive, in Florentine history.