Some teachings identified with gnosticism may have emerged before Christianity did. Others may have developed apart from Christianity, in heterodox Jewish circles, and then been adapted by groups that considered themselves to be Christian. From the 2nd through the 4th century, Christian writers catalogued and condemned certain teachers and teachings as gnostic, and the struggle to distinguish orthodox Christianity from heresies helped those writers clarify the essential beliefs and practices handed down by Christ and his Apostles to the church.