Firstly, Dan Browns writings are completely false, they are fiction and no more.
Secondly, the idea that the church is hiding things is slightly outmoded. Certainly between 200-1700AD, the church attempted to eradicate the world of anything that did not support its views, but the Industrial Revolution did for that. Prior to then, the establishment across Europe was happy to maintain the status quo, and wealthy old money families knew that their places were secured if they did not challenge the church (you scratch my back, I'll scratch yours), but the Indus Rev created a whole new breed of wealthy business people who liked to use their money to gain any knowledge (whether Biological challenges to the idea of 'humours' causing ills - hence, books like Frankenstein, and Burke and Hare robbing graves and killing people, the old Alchemy of Hermes Trimagistratus, and Euclidean mathematics - all banned by the RC church).
This brought about the Renaissance (the Medici's being famous for getting Florence in Italy excommunicated on 14 different occassions and supplying 2 popes). The Medicis compiled a vast library of books, many outlawed by the church, including copies of the Gnostic and Coptic Gospels, also the works of the great Greek philosophers and writers - Aeschylus, Sappho, Aristotle, Pythagoras and Euclid. Many people are unaware that Archimedes was a great inventor - not just a streaker - who developed weapons used by the citizens of Syracuse to defaet the Roman navy several times, and that the Greeks had steam power and railway tracks.
In fact, everything in Leonardo Da Vincis notebook is the work of previous minds. Da Vinci invented nothing, what he did do (which is a great achievement in itself) was to create modern technical drawings for Greek works which had largely been lossed. He gathered details and mentions of items in literature, pieced them together, and gave us modern working schematics for them.