Above all, he has the bishop's registers.

For a long time historians foolishly imagined that kings and wars and
parliaments and the jury system alone were history; they liked
chronicles and Acts of Parliament, and it did not strike them to go and
look in dusty episcopal archives for the big books in which medieval
bishops entered up the letters which they wrote and all the complicated
business of running their dioceses. But when historians did think of
looking there, they found a mine of priceless information about almost
every side of social and ecclesiastical life. They had to dig for it of
course, for almost all that is worth knowing has to be mined like
precious metals out of a rock; and for one nugget the miner often has to
grub for days underground in a mass of dullness; and when he has got it
he has to grub in his own heart, or else he will not understand it. The
historians found fine gold in the bishops' registers, when once they
persuaded themselves that it was not beneath their dignity to grub
there. They found descriptions of vicarages, with all their furniture
and gardens; they found marriage disputes; they found wills full of
entertaining legacies to people dead hundreds of years ago; they found
excommunications; they found indulgences to men for relieving the poor,
repairing roads, and building bridges, long before there was any poor
law, or any county council; they found trials for heresy and witchcraft;
they found accounts of miracles worked at the tombs of saints and even
of some quite unsaintly people, such as Thomas of Lancaster, and Edward
II, and Simon de Montfort; they found lists of travelling expenses when
the bishops rode round their dioceses; in one they even found a minute
account of the personal appearance of Queen Philippa, then a little girl
at her father's Court at Hainault, whom the Bishop of Exeter had been
sent to inspect, in order to see if she were pretty and good enough to
marry Edward III: she was nine years old, and the bishop said that her