Constantin von Tischendorf rediscovered the Codex Sinaiticus, a 4th-century great uncial codex of the Bible in Greek, in Saint Catherine's Monastery, Egypt.

Lobegott Friedrich Constantin (von) Tischendorf was a German biblical scholar. In 1844, he discovered the world's oldest and most complete Bible dated to around the mid-4th century and called Codex Sinaiticus after Saint Catherine's Monastery at Mount Sinai.

The Codex Sinaiticus, also called the Sinai Bible, is a fourth-century Christian manuscript of a Greek Bible, containing the majority of the Greek Old Testament, including the deuterocanonical books, and the Greek New Testament, with both the Epistle of Barnabas and the Shepherd of Hermas included. It is designated by the siglum א‎ [Aleph] or 01 in the Gregory-Aland numbering of New Testament manuscripts, and δ 2 in the von Soden numbering of New Testament manuscripts. It is written in uncial letters on parchment. It is one of the four great uncial codices. Along with Codex Alexandrinus and Codex Vaticanus, it is one of the earliest and most complete manuscripts of the Bible, and contains the oldest complete copy of the New Testament. It is a historical treasure, and using the study of comparative writing styles (palaeography), it has been dated to the mid-fourth century.

The great uncial codices or four great uncials are the only remaining uncial codices that contain the entire text of the Bible in Greek. They are the Codex Vaticanus in the Vatican Library, the Codex Sinaiticus and the Codex Alexandrinus in the British Library, and the Codex Ephraemi Rescriptus in the Bibliothèque nationale de France in Paris.

Saint Catherine's Monastery, officially the Sacred Autonomous Royal Monastery of Saint Catherine of the Holy and God-Trodden Mount Sinai, is a Christian monastery located in the Sinai Peninsula of Egypt. Located at the foot of Mount Sinai, it was built between 548 and 565, and is the world's oldest continuously-inhabited Christian monastery.