The most famous Greek manuscript of the Homeric Iliad, Venetus A, is regarded by some as the best text of the epic. It also preserves several layers of annotations, glosses, and commentaries known as the "A scholia." These are thought to preserve editorial comments made by scholars at the Royal Library of Alexandria centuries earlier. The manuscript, which was most probably written in Constantinople, also includes a summary of the early Greek Epic Cycle which is considered the most important source of information on those lost poems.
"At some point Venetus A was transported to Italy, but how and when this happened is uncertain. At one point it was thought that Giovanni Aurispa brought it there. In 1424, in a letter to [Ambrogio] Traversari in Venice, he mentioned four volumes which he had brought back from Greece:
Aristarchum super Iliade in duobus voluminibus, opus quoddam spatiosum et pretiosissimum; aliud commentum super Iliade, cuius eundem auctorem esse puto et illius quod ex me Nicolaus noster habuit super Ulixiade.
Aristarchus on the Iliad in two volumes, a large and very precious work; another commentary on the Iliad; I think Aristarchus was the author of that, as well as of the one on the Odyssey that our friend Niccolò Niccoli got from me.
"Venetus A came into the possession of Cardinal Bessarion, the Greek immigrant and scholar, and the man most directly responsible for the Western rediscovery of Greek literature in the Renaissance. Bessarion collected over a thousand books in the fifteenth century, including the only complete text of Athenaios' Deipnosophistai; the autograph of Planudes' Greek Anthology; and Venetus A.
"In 1468 Bessarion donated his library to the Republic of Venice, and the library was increased by further acquisitions from Bessarion until his death in 1473. This collection became the core of the Biblioteca Marciana. Bessarion made a condition that scholars wishing to consult the library should deposit books, but no attempt to enforce this was made until 1530.
"After that, Venetus A was largely forgotten until Villoison rediscovered and published it, along with the "B scholia" from Venetus B, in 1788. This was the first publication of any Iliadic scholia other than the "D" scholia (the scholia minora). The A and B scholia were a catalyst for several new ideas from the scholar Friedrich August Wolf. In reviewing Villoison's edition, Wolf realised that these scholia proved conclusively that the Homeric epics had been transmitted orally for an unknown length of time before appearing in writing. This led to the publication of his own seminal Prolegomena ad Homerum, which has set the agenda for much of Homeric scholarship since then" (Wikipedia article on Venetus A, accessed 01-31-2010).
In May 2007 the Venetus A manuscript was scanned at very high resolution in 3-dimensions at the Bibliotheca Marciana. That technical process was described in Wired Magazine.
♦ You can view a high-resolution 2-dimensional digital facsimile of the manuscript, including details of significant areas and ultraviolet images of badly faded text, from the website of the Center for Hellenic Studies of Harvard University at this link.