Turning to the question of the origin of the University of Oxford, it may be noted that though many mythical origins trace the existence of the university to a very early time in the history of the country, yet, in fact, Oxford did not become known as a centre of learning until the twelfth century. The earliest definite reference, which has been traced so far to the existence of any school at Oxford, dates to some time in the decade 1110-1120, when Theobald of Etampes is described as a "Master of Arts at Oxford."[398] Apparently, Thurstan, Archbishop of Canterbury, had referred to Theobald the question whether monks could legally impropriate churches and tithe. His reply was in the negative on the ground that the monk was one who had retired from the world, and "by choosing the monastic habit and putting the world aside had judged himself unworthy of the dignity of an ecclesiastic."[399] This provoked an anonymous reply which incidentally contains the statements that Theobald held a scholastic post of some importance. "You, yourself, a nobody, are you not said to have taught as a master sixty or one hundred clerks, more or less?"[400] This statement supports an hypothesis that the schools at Oxford must have been flourishing at the time. A new era in the development of Oxford may be traced from C. 1135 when Robert Pullen, a theologian, lectured there.[401] Then, at a date between 1145 and 1150, the jurist Vacarius, "a Lombard by birth, an upright man and a lawyer," was teaching Roman Law somewhere in England.[402] At some time or other he also taught at Oxford and is stated to have been the first to teach Roman Law in that city.[403] The university must be regarded as being fully in existence by 1189, as Giraldus Cambrensis lectured there about that date on "Ireland" to "all the doctors of the different faculties and such of their pupils as were of greater fame or note" on one day, and to the "rest of the scholars" on another.[404] After this date, the references are numerous and conclusive.