In fact, on February 3, 1182, the people of Empoli were reduced to submission, bound over to pay annual tribute and to yield military service at the request of the Florentine Consuls, whether of the Commune or the Guilds, save in the event of a war against the Counts Guidi.[174] The people of Pogna, which was a fief of the Alberti,[175] were the next to make surrender on the 4th of March. And these Pognesi not only pledged themselves to take the field at the command of the Florentine Consuls, but to abstain from constructing new walls or fortresses, either on their own territory or the neighbouring lands of Semifonte. Also, should others attempt to fortify those places, they (the Pognesi) were bound to oppose it and give notice of the fact to the Florentines, who, on their side, promised friendship and protection.[176] In the same year the Castle of Montegrossoli was captured by the Florentines.[177] On July 21, 1184, they made an alliance with the people of Lucca, who promised to send them yearly a contingent of one hundred and fifty horse and five hundred foot, for at least twenty days' service, in all wars waged within Florentine territory.[178] In October the Florentines attacked the Castle of Mangona in the Mugello, but as this fortress belonged to the Alberti, the latter stirred Pogna to rebellion, and the Florentines quickly marched against that town.[179] Count Alberti seems to have taken part in the fight that ensued at Pogna, for it is known that by November he was in captivity and forced to accept very hard terms for himself, his wife and his children. He had to promise to dismantle his fortress of Pogna the following April, only retaining his own palace and tower; to demolish the tower of Certaldo, and never rebuild that of Semifonte. He was to cede to the Florentines whichever one of the Capraia towers they chose to take; he was to give them one-half of the ransom or tax to be levied on all his possessions in general between the Arno and the Elsa. Finally, as soon as he should be released from prison ("_postquam exiero de prescione_"), he was pledged to compel all his men to swear fealty, and to the payment of four hundred pounds of good Pisan money. His sons were to reside in Florence two months of the year in time of war, one month in time of peace.[180] The subjection and humiliation of this Count Alberto was a very significant fact in itself. And when we reflect that it occurred after Florence had already overthrown the Cadolingi, lowered the power of the Guidi house, and concluded most favourable alliances with Pisa, Sienna, and Lucca, it will be easily seen how quickly the Commune had been able to soar to a position of very great and almost menacing strength. IV.