The Codex Sinaiticus is one of the oldest versions of New Testament that exists today. This version was originally written in Greek.
In 1844 German Bible scholar Constantin Tischendorf went to the famous Greek Orthodox monastery of Saint Catherine. The monastery is located near a mountain in the Sinai desert where Moses is believed to have received the law (archaeologists and historians have a lot of disputes about this claim to this day).
There are several stories about how Tischendorff stumbled upon the manuscripts. One version of the story says that he saw some pages that the monks were about to burn. Another version claims that he found them in the trash. No matter the origin story, Tischendorf did find a Greek Bible from either fourth or fifth century (Codex Sinaiticus stands for “The Book From Sinai“). It had large portions of the Greek Old Testament, a complete New Testament, and some extra writings, too. These extra writings later became known as the books by Apostolic Fathers.
Tischendorf came back to the monastery in 1859 with funds he obtained from the Tsar of Russia and persuaded the monastery to sell the book to the Russian Tsar. To this day the monks claim that they have a note from Tischendorf with a promise to return the book.
In 1933, after the Soviet revolution, Lenin sold the manuscript to the British Museum, where you can find it on display to this day. Some scholars believe that Codex Sinaiticus is one of the fifty Bibles that Emperor Constantine had produces for the largest fifty churches of his capital city, Constantinople.
The extra writings are the Epistle of Barnabas and the Shepherd of Hermas. Their presence in the Codex Siniaticus suggests that some early versions of the Bible included them together with other books.