LONDON — The surviving pages of the world's oldest Christian Bible have been reunited — digitally.

The early work, known as the Codex Sinaiticus, has been housed in four separate locations across the world for more than 150 years. Starting Monday, it became available for perusal on the Web at www.codexsinaiticus.org so scholars and other readers can get a closer look at what the British Library calls a "unique treasure."

Scot McKendrick, head of Western manuscripts at the British Library, said the book "offers a window into the development of early Christianity and firsthand evidence of how the text of the Bible was transmitted from generation to generation."

The 4th-century book, written in Greek on parchment leaves, has been housed in four separate locations across the world for more than 150 years. It has been digitally reunited in a project involving organizations from Britain, Germany, Russia, and Egypt, each of which possessed parts of the 1,600-year-old manuscript.

They worked together to publish new research into the history of the Codex and transcribed 650,000 words over a four-year period.

Juan Garces, the Codex Sinaiticus project manager, said it was a "definitely a historical moment."

The Codex was both a key Christian text and "a landmark in the history of the book, as it is arguably the oldest large bound book to have survived," McKendrick said.

Codex Sinaiticus, which, loosely translated, means "the book from Sinai," was discovered at the Monastery of Saint Catherine at Mount Sinai by German Bible scholar Constantine Tischendorf in the mid-19th century. Much of it eventually wound up in Russia — just how exactly the British Library won't say, citing lingering sensitivity over the circumstances surrounding its removal from the monastery.

The British Library bought 347 pages from Soviet authorities in 1933. Forty-three pages are at the University Library in Leipzig, Germany, and six fragments are at the National Library of Russia in St. Petersburg. And in 1975, monks stumbled on 12 more pages and 40 fragments stashed in a hidden room at the monastery at Mount Sinai.

Garces said the only other Bible that rivals Codex Sinaiticus in age is Codex Vaticanus, which was written around the same time but lacks parts of the New Testament. Codex Sinaiticus is the oldest book that contains a complete New Testament and is only missing parts of the Old Testament and the Apocrypha.