Paolo manuscript

A parchment kept by Paolo of Genoa perhaps from the mid-13th century. It was hidden among other documents in a tin box secreted in a wall of St. Sophia in Constantinople. Its most significant manuscript represents a stained glass window and Roman numerals. The reverse side of the parchment has a writing in the Coptic alphabet, appearing to be some sort of cipher. On its top there is a crude drinking vessel with the Aramaic words ‘father, son, holy ghost.’ It also referred that the Holy Grail was guarded by a lethal protective device.

G. Codirolli discovered the tin box. Knowing about Henry Walton Jones, Senior's quest about the Holy Grail, he offered to show it to him. On his way to lecture in America he traveled onboard the Titanic; he survived the wreck, and salvaged the precious document. He stopped by Las Mesas and delivered the document to Dr. Jones allowing him to make a facsiile before he returned after his lecture to the west coast.

Behind the scenes
The drawing referred in the description must be related to a puzzle in the Indiana Jones and the Last Crusade: The Graphic Adventure, where Indy has to locate the correct stained glass window in the Biblioteca di San Barnaba. The image of the window does not appear in the game documentation, but appears only on-screen in the game. The exact drawing is random among six possible images.

The "Coptic cipher" is referred two more times in the game documentation by Henry. Hearing about the Coptic Gospel of Joseph of Arimathea he hopes to find some clue about it, however the text of the "Diary" leaves this matter unanswered, and the cipher is neither mentioned in the game. It is possible however that the "cipher" is an obscure reference to the copy protection of the game, as the package contains a sheet with combinations of Coptic characters; these form the code that Indy must show to Indy near the beginning of the game.