According to the Catholic Encyclopedia, Elcesaites were a sect of Gnostic Ebionites, whose religion was a wild medley of heathen superstitions and Christian doctrines with Judaism. Hippolytus (Philosophumena, IX, 13-17) tells us that under Callistus* (217-222) a cunning individual called Alcibiades, a native of Apamea in Syria, came to Rome, bringing a book which he said had been received from Parthia by a just man named Elchasai (’Elchasaí; but Epiphanius has ’Elksaí and ’Elkessaîoi; Methodius, ’Elkesaîos, and Origen, ’Elkesaïtaí). The contents of the book had been revealed by an angel ninety-six miles high, sixteen miles broad, and twenty-four across the shoulders, whose footprints were fourteen miles long and four miles wide by two miles deep. Read on.
*Callistus was the Bishop of Rome.
Related is Catholic Encyclopedia: Apocrypha, A long article with a comments on each Apocryphal book. Classified according to origin, and the e-text Apocryphal Acts of The Apostles, Edited From Syriac Manuscripts in The British Museum and Other Libraries by W. Wright, LL.D., Ph. D., 1871.
JSTOR has an article The Acts of the Apostles by A.F.J. Klijn.