St. Patrick is perhaps the most venerated saint of the modern age, whose feast day is marked each year by massive celebrations across the world, from Dublin to New York and Sydney to Rio de Janeiro. In spite of his popularity very little is known of his life, which is clouded by myth and uncertainty. The facts that are known--that he was born in the late fourth century in Roman Britain, was captured by Irish raiders at the age of 16 and sold into slavery, and escaped six years later to Britain where he became a priest and later a bishop before returning to Ireland to proselytize--give only...