The codex in fact contained a complete copy of the New Testament in addition to most of the Old Testament in Greek (though portions were missing, because the monks had periodically used pages from the codex as kindling, as von Tischendorf had already discovered, to his horror, on one of his previous visits) as well as copies of some extra-biblical manuscripts, some of which were previously known only in Latin translations (The Epistle of Barnabas) or in name only (The Shepherd of Hermas). This mid-fourth century AD manuscript, which became known as Codex Sinaiticus, is still the oldest known manuscript of the complete New Testament in existence.
Von Tischendorf, being permitted to freely peruse the manuscript that evening, his last in the monastery, stayed up all night reading it. He recorded in his diary – kept in Latin, like a true scholar – “quippe dormire nefas videbatur – needless to say, to sleep seemed like a crime.” After much diplomatic wrangling, the manuscript was allowed to leave the monastery for study and copying. Today portions of the Codex reside in various places: Leipzig University, The British Library, and the National Library of Russia in Saint Petersburg. In 1975, during restoration work at the monastery, a forgotten room was discovered below a chapel in which were found many parchment fragments and 12 additional complete leaves of the Codex Sinaiticus, which remain at the monastery.
In addition to its importance as an early biblical manuscript, it is also an outstanding example of scribal craftsmanship, as Robert Bringhurst as pointed out. The text is written with a very even hand in resplendent Greek uncial script, arranged in four narrow columns on each page. Careful analysis of the proportions used in the layout reveal a scheme of exceptional cleverness and subtlety – just the kind of game that scribes, typographers, and designers at the height of their craft have enjoyed playing for millennia. The four columns considered as a complete text block express the reciprocal proportions of the surrounding page (that is, they are in the same proportions, but rotated 90 degrees). But, almost miraculously, if one were to remove the gutters between the columns, the entire textblock would collapse into a rectangle in unison with the page itself (same proportions, in the same orientation, just at a smaller size)!