This First, or Old Popular Government, as it was called, because it was in fact the first time that the people had a political and military organisation of their own, quickly asserted its strength. In order to give the spreading Florentine trade free access to the sea, without yet coming to blows with Pisa, the city concluded an agreement on April 30, 1251, with the Counts Aldobrandeschi, powerful lords of the Maremma, by which Florence was granted right of passage through their territories to Porto Talamone and Port' Ercole and the free use of these harbours for its merchandise.[252] Thereupon the Pisans, being naturally annoyed by this measure, hastened to contract an alliance with Sienna, to which Pistoia also adhered. Thus the three Ghibelline cities were banded together against the Florentine Guelphs. Nor was this the worst. On July 24, 1251, the Ghibellines of Florence joined the League by a secret agreement with Sienna, binding either side to cooperate towards their common aim--_i.e._, the triumph of their party throughout Tuscany. And as the other Ghibellines of the country-side naturally adhered to the treaty, the whole faction was united to the hurt of the Republic. Then the Florentines, finding themselves surrounded by so many foes, began their defence by a rapid march on Pistoia, but the Ghibellines of the city refused to take part in a war openly directed against their cause. Accordingly, when the army returned from a successful skirmishing expedition, many leading Ghibellines, including the Uberti and the Lamberti, were driven into banishment. The affair must have been really serious, for the exiles hoisted the banner of the Republic, whereupon the State banner was changed, and instead of bearing the white lily on a red field, henceforth displayed the red lily on a white field; but the flag of the people remained as before, half white and half red. During the summer of this year the Ubaldini, reinforced by a body of exiles, rose to arms in the Mugello, but suffered defeat. The Florentines at last realised the danger of their position. Therefore, with the help of their former friends the Lucchese, they concluded an alliance (August, 1251) with the town of San Miniato al Tedesco--where there was no Imperial vicar for the moment--renewed in September their former treaty with Orvieto, and in November made alliance with Genoa, which was still hostile to Pisa.