Forces that tended to make Paris one of the most important cities of transalpine Europe were in operation at this time; hence the stream of pilgrim students to Paris, which set in in the days of Abelard, continued for at least one and a half centuries.[395] At this time, too, the tendency for those who had interests in common to associate in some form of "gild," was everywhere prevalent. It was, therefore, only natural that wherever a concourse of masters or students was found, the necessity soon arose for some form of organisation, which would serve to protect their common interests. Though these organisations came into existence without any express authorisations, yet from such beginnings the universities of the Middle Ages originated. The circumstances, which contributed to the formation of a medieval university were therefore twofold: (1) the existence of a cathedral school, or monastic school, which had attained eminence, and (2) the formation of a gild, either of masters, or of students, or of both. Special circumstances led to the selection of the original university centres. One of these circumstances was the specialisation of the learning of the time. A mass of learning and tradition on subjects of interest to man and essential to his welfare, had grown up in a particular locality. Students who desired to possess themselves of this knowledge were attracted to the place. Thus, the schools at Bologna developed into specialised law schools about 1100 to 1130; Salerno became famous for the study of medicine; Paris became celebrated as the main centre of scholastic philosophy. It must be noted, however, that the term "universitas" was not the common appellation for one of the higher schools; the earliest specialised name was "studium" or "studium generale"--a term that Denifle has traced back as far as 1233. At the outset, no restriction upon the establishment anywhere of a "studium generale" existed, but by the latter half of the thirteenth century this unrestricted liberty came to an end. The idea gradually grew that the erection of new "studia generalia" was a papal or imperial prerogative; hence in 1224 the Emperor Frederick II. founded a "studium generale" at Naples; in 1229 Gregory IX. established one at Toulouse, whilst in 1244 or 1245 Innocent III. founded a "studium generale" in the Pontifical Court itself.[396] In 1292 even the old universities--Bologna and Paris--received formal recognition of their existence by Bulls of Nicholas IV. "From this time, the notion gradually gained ground that the 'jus ubique docendi' was of the essence of a 'studium generale,' and that no school which did not possess this privilege could obtain it without a Bull from Emperor or Pope."[397]