 Others set other dates or time periods when the Church corrupted itself, making it necessary for them to leave the Roman Catholic Church in order to re-establish the true Church.Several descendant groups, including Baptists and Mennonites, believe that besides the Great Apostasy there has also always been a "little flock", a "narrow way" which struggled through persecution and remained faithful to the truth.For example, the Mennonites published a book called the "Martyrs Mirror" in 1660 that attempted to show that exclusive Believer's baptism was practiced and passed down in every century, and how those who held that belief were persecuted for it.