The Life of Cesare Borgia by Rafael Sabatini

At the time of his father's election to the throne of St. Peter, Cesare Borgia--now in his eighteenth year--was still at the University of Pisa.

It is a little odd, considering the great affection for his children which was ever one of Roderigo's most conspicuous characteristics, that he should not have ordered Cesare to Rome at once, to share in the general rejoicings. It has been suggested that Alexander wished to avoid giving scandal by the presence of his children at such a time. But that again looks like a judgement formed upon modern standards, for by the standards of his day one cannot conceive that he would have given very much scandal; moreover, it is to be remembered that Lucrezia and Giuffredo, at least, were in Rome at the time of their father's election to the tiara.