Book of Thoth?
Taking control of the parchment to fly out of the box, Arthur held the letter in his hand looking at its contents with knowledge
"The book of Thoth, a representative of his power"
"The recorder of knowledge"
"The one who flows with the river of time"
"The one who watches the day end and seasons begin"
"The one who watches the seed being planted, and sees it wither"
" For he recorded the beginning, foretold the future, and witnessed the end"
"The one who finds the book of Thoth shall become the new Thoth!"
Reading through the parchment, although it wasn't much but Arthur already got the gist of most of it
According to what was written there, the original Thoth for some reason is either dead or missing, however, his book remains
That book is what holds his power, meaning even if a mortal got it, then he could potentially on the spot become a god