Though the folded note tablets used by the Greeks and Romans may have suggested the codex form, its development to eventual supremacy was related to cultural and technological changes—i.e., the rise of Christianity, with its demand for more and larger books, and the availability of first parchment and then paper. The oldest extant Greek codex, said to date from the 4th century, is the Codex Sinaiticus, a biblical manuscript written in Greek (see photograph-->). Also important is the Codex Alexandrinus, a Greek text of the Bible that probably was produced in the 5th century and is now preserved in the British Library, London. The term codex aureus describes a volume with gold letters written on sheets that have been stained with a purple dye called murex. Existing examples of the codex aureus date from the 8th and 9th centuries.