The free popular element, or middle class, which had been reborn in the preceding period with the founding of the _villas_, or _concejos_, developed a much greater social importance than formerly. Many factors contributed to this end, such as the increase in the number of the _villas_, the concession of new privileges, the material advance of Christian Spain (agriculturally, industrially, and commercially), the important military services of the municipal militia, and the fact that not only the _caballeros_ but also the leading jurisconsults began to be recruited from the middle class. As a rule this element paid taxes, but it enjoyed not a few exemptions and privileges,--for example, a right not to be required to make unusual contributions at the mere will of the king, or in some cases a right to commute all of their taxes to a single tribute. At the same time, the servile classes made striking advances, in part through their own efforts, but aided also by an increasing sentiment in favor of manumissions, by the need for population (both as a result of the conquests and in consequence of economic development), and by the protection accorded them in the _villas_. The movement for emancipation was not uniform or free from setbacks, and this led to numerous uprisings of serfs, who joined the enemies of their masters in wars against the latter. The monks of Cluny, accustomed to the much greater subjection of the servile classes in France, represented a strong current of reaction. At Sahagún, the principal Cluniac centre, there were such limitations on liberty as those requiring that all bread must be cooked in the ovens of the monastery, and forbidding anybody to sell his wine before the monks had sold theirs, or to buy cloth, fresh fish, firewood, or other necessities before the monks had bought theirs, and there were other restrictions of a like character. By the end of the twelfth century serfs generally had gained such rights as the exact fixing of services due their lords, the abolition of the practice of selling them with the land, and the recognition of the validity of their marriages, whether consented to by their lords or not. In the thirteenth century they gained almost complete personal liberty, doing away with the _malos usos_, or bad customs, like those referred to in the case of the monastery of Sahagún. [Sidenote: The four new social classes.]