Apocrypha
There is no question that these books have always been part of the Bible in Oriental Orthodox Churches, so they were definitely not added in the 1500s. Around the year 80 AD, the Jewish Council (Sanhedrin) decided to cut the books from the Hebrew Bible, but they stayed in the Christian Bible. Then soon after Christianity became the only religion of Roman Empire in the 4th century, the Romans decided to cut out all of the same books that the Sanhedrin had cut out, and they moved some of them to the "apocrypha".