The Codex Climaci Rescriptus
The Codex is an example of one of the funnest literary terms I've heard in a while: it is a palimpsest. In ancient times, due to the difficulty in acquiring or affording parchment, old documents were reused. Being rather thick and resilient, the top layer of the parchment was literally scraped off, leaving a mostly-clean sheet to be written upon again. The process wasn't perfect, and as you see in the example above, the Codex had a very ineffective erasing. A ghost of the original text is clearly visible through the new transcription, and has been identified as portions of the New Testament. The biblical stories were scraped off, and in the 9th century A.D. the pages were flipped and re-written with a portion of the Scala Paradisi and Liber ad Pastorem. Today, those add far less to the value than the underlying older text: the Codex is better known for its Bible text than anything else.