Some of the rarest and most fragile religious texts in the Vatican and Bodleian libraries, including ancient bibles and some of the oldest Hebrew manuscript and printed books, are being placed online in a joint project by the two great libraries, which will eventually create an online archive of 1.5m pages.

The website launched on Tuesday with funding from the Polonsky Foundation includes the first results of the four-year project, including the Bodleian's 1455 Gutenberg Bible, one of only 50 surviving copies of the first major book printed in the west with metal type.

The site will also host a growing collection of scholarly essays, and interviews with the Oxford and Vatican librarians, and the Archbishop of Canterbury, Justin Welby, who said the digitisation was of huge international significance.

"Where you can see these ancient texts there is just a lifting of the spirits … I think those who did the printing in the past would think the scanning was a very considerable improvement, it must have been very hard work. Essentially the scanners of today and the printers of the past are engaged in very similar work."

The two institutions are equally venerable. The Vatican library was founded in 1451 by Pope Nicholas V for "the common convenience of the learned", while the Bodleian opened to scholars in 1602 but incorporated Duke Humfrey's library of 1488, and including much older collections.

The two libraries hold material which was originally in the same collections, or even the same volumes, so the four-year project will reunite material separated for centuries.

The works to be digitised include the small but staggering collection of Greek manuscripts in the Vatican, including ancient texts of works by Homer, Sophocles, Plato and Hippocrates. The Bodleian's collection is much larger – by the end of the 17th century the most important in Britain – but later, mainly of 15th and 16th century manuscripts.

The Vatican's Hebrew texts include the oldest Hebrew codex – a manuscript bound as a book – in existence, and a copy of the entire Bible written in Italy around 1100. The Vatican's collection of 8,900 incunabula – the earliest printed books, many published in Rome – is the fourth largest in the world, followed closely by the Bodleian's.