Codex Sinaiticus is one of the oldest known manuscripts of the Christian Bible, dating back to the 4th century. It contains the complete text of the New Testament and a significant portion of the Old Testament, written in Greek. This ancient manuscript is highly valued for its historical and textual significance, providing insights into early Christianity and biblical texts. Discovered in the Saint Catherine's Monastery at the foot of Mount Sinai in Egypt, Codex Sinaiticus is considered a critical resource for scholars studying the development of the Bible. Today, it is housed in various institutions, with significant portions held at the British Library in London.