Was Peter really crucified upside down by the Romans?

Many Christians today believe in a long-held tradition that Peter was crucified upside down by the Romans.  This was done because he did not consider himself worthy to die the same way Christ died.  However, this tradition is based on a Gnostic work known as the Acts of Peter, written sometime around 100-200 AD.  Eusebius also states that Peter died by crucifixion, but while he is considered an authority on early church history, his sources and skills as a historian are questionable.  There is no Biblical evidence of Peter ever in Rome, even though we see him in Babylon (1 Peter 5:13); and while some claim this is symbolic of Rome, as found in Revelation 17, the book of 1 Peter does not use the same symbolism and style of Revelation.  This tradition was formulated to give credence to the idea that Peter was a bishop at Rome and to give Rome prominence, even though there is no historical evidence of this belief.