I'm still in the thrall of one insatiable desire, which hitherto I have been neither able nor willing to check. ... I cannot get enough books. It may be that I have already more than I need, but it is with books as it is with other things: success in acquisition spurs the desire to get still more. ... Books delight us through and through, they talk with us, they give us good counsel, they enter into a living and intimate companionship with us. ... Now do you, as you hold me dear, commission trustworthy and competent men to go through Tuscany for me, examining the book-chests of the religious and of other studious men, searching for things that might serve to alleviate or to increase my thirst. And although you know in what streams I fish and in what woods I hunt, nevertheless, to avoid error I enclose a list of the things I chiefly desire; and that you may be the more eager, let me tell you that I am sending similar requests to friends in Britain, France, and Spain. So then, in order that none may surpass you in faithfulness and diligence, do your best — and farewell.
From a letter from Petrarch to the Dominican friar Giovanni dell'Incisa in 1346. This translation by Ernest Hatch Wilkins quoted in Introduction to Manuscript Studies by Raymond Clemens & Timothy Graham, who go on to say that if Petrarch "could not acquire the books he wanted by purchase or gift, he would arrange to have them copied by professional scribes. It has been estimated that by the end of his life he had accumulated a personal collection of some 200 volumes" (64).
All told, my library is probably double the size of Petrarch's, and I've put (comparatively) little effort into finding the books I want or for which I experience a passing whim. I'd imagine Petrarch's head would a-splode if he walked into the library at Brown, which contains over 2,000,000 volumes. Let's take a minute to cheer for the spread of printing technology and literacy over the past 600 years! Whoo-hoo!!