* Bank was founded more than 500 years ago * Dominates life in and around Siena * Trading losses could reach nearly $1 billion By Silvia Aloisi SIENA, Italy, Jan 25 (Reuters) - When the Monte dei Paschi di Siena bank was founded in 1472, Michelangelo was not born, Columbus had still to discover America and Henry VIII of England had yet to split from the church of Rome.