<P> The oldest extant depiction of the execution of Jesus in any medium seems to be the second - century or early third - century relief on a jasper gemstone meant for use as an amulet, which is now in the British Museum in London . It portrays a naked bearded man whose arms are tied at the wrists by short strips to the transom of a T - shaped cross . An inscription in Greek on the obverse contains an invocation of the redeeming crucified Christ . On the reverse a later inscription by a different hand combines magical formulae with Christian terms . The catalogue of a 2007 exhibition says: "The appearance of the Crucifixion on a gem of such an early date suggests that pictures of the subject (now lost) may have been widespread even in the late second or early third century, most likely in conventional Christian contexts". </P> <P> The Jewish Encyclopedia says: </P> <P> The cross as a Christian symbol or "seal" came into use at least as early as the second century (see "Apost . Const ." iii. 17; Epistle of Barnabas, xi. - xii.; Justin, "Apologia," i . 55 - 60; "Dial . cum Tryph ." 85 - 97); and the marking of a cross upon the forehead and the chest was regarded as a talisman against the powers of demons (Tertullian, "De Corona," iii.; Cyprian, "Testimonies," xi. 21--22; Lactantius, "Divinæ Institutiones," iv. 27, and elsewhere). Accordingly the Christian Fathers had to defend themselves, as early as the second century, against the charge of being worshipers of the cross, as may be learned from Tertullian, "Apologia," xii., xvii., and Minucius Felix, "Octavius," xxix . Christians used to swear by the power of the cross </P> <P> Catholics, Orthodox Catholic, Oriental Orthodox, members of the major branches of Christianity with other adherents as Lutheranism and Anglicans, and others often make the Sign of the Cross upon themselves . This was already a common Christian practice in the time of Tertullian . </P>

Where did the term double cross come from