More than once in the course of Frederick's career it seemed as if he might become master of Tuscany in fact as well as in name, had Florence only been as well affected to him as were Siena and Pisa. But already, as has been said, the popular interest had been strengthened by accessions from among the nobles. Others of them, without descending into the ranks of the citizens, had set their hopes on being the first in a commonwealth rather than privates in the Imperial garrison. These men, with their restless and narrow ambitions, were as dangerous to have for allies as for foes, but by throwing their weight into the popular scale they at least served to hold the Imperialist magnates in check, and established something like a balance in the fighting power of Florence; and so, as in the days of Barbarossa, the city was preserved from taking a side too strongly. The hearts of the Florentine traders were in their own affairs--in extending their commerce and increasing their territory and influence in landward Tuscany. As regarded the general politics of Italy, their sympathy was still with the Roman See; but it was a sympathy without devotion or gratitude. For refusing to join in the crusade of 1238 the town was placed under interdict by Gregory IX. The Emperor meanwhile was acknowledged as its lawful overlord, and his vicar received something more than nominal obedience, the choice of the chief magistrates being made subject to his approval. Yet with all this, and although his party was powerful in the city, it was but a grudging service that was yielded to Frederick. More than once fines were levied on the Florentines; and worse punishments were threatened for their persevering and active enmity to Siena, now dominated by its nobles and held in the Imperial interest. Volunteers from Florence might join the Emperor in his Lombard campaigns; but they were left equally free by the Commonwealth to join the other side. At last, when he was growing old, and when like his grandfather he had been foiled by the stubborn Lombards, he turned on the Florentines as an easier prey, and sent word to the nobles of his party to seize the city. For months the streets were filled with battle. In January 1248, Frederick of Antioch, the natural son of the Emperor, entered Florence with some squadrons of men-at-arms, and a few days later the nobles that had fought on the popular side were driven into banishment. This is known in the Florentine annals as the first dispersion of the Guelfs.