>
> However, in my recreational searching, I have found the oldest Euclid
> in existence is in the Vatican library, which I saw on tour, from the
> 800's. However, I have heard at least four people say that they saw
> the oldest Euclid somewhere else.
>
"Oldest" has two meanings in this context. The text in the Vatican Library
(Cod. Vat. graec.190) does not contain the addition of Theon of Alexandria
to Prop. VI.33 that Theon identified in a commentary he wrote to the almagest.
As he, Theon, has made a "critical edition" (my English isn't good enough to
express what I really want to say) of Euclid's elements, one believes that
the text in the Vatican is older than the text Theon prepared. Theon's version
of the elements seems to underly all the other known texts. Hence the text in
the Vatican is the oldest known complete text of the elements. The manuscript
itself was written in the 10th century.
There is a text in the Bodleian Library which was written in 888 by the
Byzantine calligrapher Stephanus for the archbishop Aretas of Kappadokia.
This seems to be the physically oldest known text of the elements. It is
based on Theon's text.
My knowledge comes from
Peter Schreiber, Euklid. Biographien hervorragender Naturwissenschaftler,
Techniker und Mediziner. Vol. 87. Leipzig 1987
Heinz Lueneburg