Hermas, or Shepherd of Hermas is an early Christian document known to the early church fathers. The Muratorian canon, a list of canonical books from about the 3rd century, says Hermas was written by the brother of Pius, Bishop of Rome, around 140-154 AD. It was most likely written in Rome. Despite much speculation, the author remains unknown.
Visions I-IV were composed during a threatened persecution, probably under Trajan (the Clement of 8:3 could be Clement of Rome). Vision V - Similitude VIII and Similitude X were written perhaps by the same author to describe repentance to Christians who were wavering. Similitude IX was written to unify the entire work and to threaten those who had been disloyal. This last phase must have occurred before Irenaeus (ca. 175). A preferred date would be 140. On the basis of this internal analysis multiple authorship seems necessary (Giet 1963), though the work could have been composed by one person over a long period of time (Joly 1958). Graydon F. Snyder (The Anchor Bible Dictionary, v. 3, p. 148)