With Federigo, successor of Duke Oddantonio, commences the proper subject of these volumes, but we are met by a preliminary difficulty as to his birth and parentage, which has baffled many of his biographers. It would be useless, as well as tedious, to enumerate and examine the host of conflicting and often inconsistent authorities on this vexed question.[55] The amount of blundering and contradiction to which it has given rise is scarcely conceivable, considering that most of our authorities either frequented the court of Urbino during his own and his son's time, or had access to contemporary documents. Seven separate theories have found supporters:--1. That Federigo was son of Count Guidantonio, born in wedlock; 2. That he was his natural, but legitimated son; 3. That he was his natural son, passed off as the child of his first wife Rengarda, after a pretended pregnancy; 4. That he was son of Bernardino della Carda and his wife Anna, sister of Count Guidantonio, adopted by the latter whilst he had no son; 5. That he was their son, passed off as the child of Countess Rengarda; 6. That he was their son, passed off as a natural child of Guidantonio; 7. That being their son, and Anna or Aura being daughter of Guidantonio, he was adopted or passed off as son of the latter, though, in fact, his grandson.[56] It would follow that he might have been either nephew, brother-in-law, or son of Bernardino. All doubt on this subject is set at rest by a formal legitimation from Martin V., of 22nd December, 1424, which I discovered in the Archivio Diplomatico at Florence, in favour of Federigo, as son of Guidantonio by a maiden of Urbino. This document is alluded to by Galli, Reposati, and others; but its existence has been often denied, notwithstanding the almost equally valid evidence of that Count's testament quoted by Riposati, wherein, failing his lawful sons, he substitutes his "legitimate son" Federigo as his universal heir. [Footnote 55: LAZZERINI, in his _Memorie Storiche dei Conti di Urbino_, has discussed without exhausting them in fifty folio pages. The magnificent work by Count Pompeo Litta is marred by adopting the theory of an Ubaldini descent for Duke Federigo. See his notice of Emilia Pio da Carpi, wife of Count Antonio di Montefeltro.]