Cross

===Post-Christian===
{{Main|Christian cross|Crucifixion}}
{{Further|Instrument of Jesus' crucifixion|Early Christian symbols|Christogram|Christian cross variants|Cross necklace}}
[[File:Solidus-Leontinus-sb1330.jpg|thumb|Early use of a [[globus cruciger]] on a [[solidus (coin)|solidus]] minted by [[Leontios]] (r. 695–698); on the obverse, a stepped cross in the shape of an [[Iota Eta]] monogram.]]

The shape of the cross (''crux'', ''[[stauros]]'' "stake, gibbet"), as represented by the letter [[Tau (letter)|T]], came to be used as a new symbol (seal) of the [[Early Christianity]] since the [[2nd century]].<ref>{{cite web |quote=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 |url=http://jewishencyclopedia.com/view.jsp?artid=899&letter=C  |title=Cross |website=[[Jewish Encyclopaedia]] |first1=Kaufmann  |last1=Kohler |url-status=live |archive-url=https://web.archive.org/web/20111007032024/http://jewishencyclopedia.com/view.jsp?artid=899&letter=C |archive-date= Oct 7, 2011 }}</ref> [[Clement of Alexandria]] in the early 3rd century calls it {{lang|grc|τὸ κυριακὸν σημεῖον}} ("the Lord's sign") he repeats the idea, current as early as the [[Epistle of Barnabas]], that the number 318 (in [[Greek numerals]], ΤΙΗ) in Genesis 14:14 was a foreshadowing (a "type") of the cross (the letter Tau) and of Jesus (the letters [[Iota Eta]]).<ref name="CA">{{cite web|url=http://www.earlychristianwritings.com/text/clement-stromata-book6.html |title=Clement of Alexandria: Stromata, Book 6 |website=Early Christian Writings |access-date=2016-06-18}}</ref> Clement's contemporary [[Tertullian]] rejects the accusation that Christians are  ''crucis religiosi'' (i.e. "adorers of the gibbet"), and returns the accusation by likening the worship of pagan idols to the worship of poles or stakes.<ref>{{cite web |url=http://www.newadvent.org/fathers/0301.htm |title=Church Fathers: Apology (Tertullian) - Chapter 16 |quote=Then, if any of you think we render superstitious adoration to the cross, in that adoration he is sharer with us. If you offer homage to a piece of wood at all, it matters little what it is like when the substance is the same: it is of no consequence the form, if you have the very body of the god. And yet how far does the Athenian Pallas differ from the stock of the cross, or the Pharian Ceres as she is put up uncarved to sale, a mere rough stake and piece of shapeless wood? Every stake fixed in an upright position is a portion of the cross; we render our adoration, if you will have it so, to a god entire and complete. We have shown before that your deities are derived from shapes modelled from the cross. |website=New Advent |translator-first1=S. |translator-last1=Thelwall |date=1885 |editor-first1=Alexander |editor-last1=Roberts |editor-first2=James |editor-last2=Donaldson |editor-first3=A. Cleveland |editor-last3=Coxe |editor-first4=Kevin |editor-last4=Knight |url-status=live |archive-url=https://web.archive.org/web/20240312152944/https://www.newadvent.org/fathers/0301.htm |archive-date= Mar 12, 2024 }} ''Sed et qui crucis nos religiosos putat, consecraneus noster erit. Cum lignum aliquod propitiatur, viderit habitus, dum materiae qualitas eadem sit; viderit forma, dum id ipsum dei corpus sit. Et tamen quanto distinguitur a crucis stipite Pallas Attica, et Ceres Pharia, quae sine effigie rudi palo et informi ligno prostat? Pars crucis est omne robur, quod erecta statione defigitur; nos, si forte, integrum et totum deum colimus. Diximus originem deorum vestrorum a plastis de cruce induci.''</ref>
In his book ''De Corona'', written in 204, Tertullian tells how it was already a tradition for Christians to trace repeatedly on their foreheads the [[sign of the cross]].<ref>"At every forward step and movement, at every going in and out, when we put on our clothes and shoes, when we bathe, when we sit at table, when we light the lamps, on couch, on seat, in all the ordinary actions of daily life, we trace upon the forehead the sign" ([http://www.ccel.org/ccel/schaff/anf03.iv.vi.iii.html ''De Corona'', chapter 3])</ref>

While early Christians used the T-shape to represent the cross in writing and gesture, the use of the [[Greek cross]] and [[Latin cross]], i.e. crosses with intersecting beams, appears in Christian art towards the end of [[Late Antiquity]]. An early example of the [[cruciform halo]], used to identify Christ in paintings, is found in the ''Miracles of the Loaves and Fishes'' mosaic of [[Sant'Apollinare Nuovo]], Ravenna (6th century). The [[Patriarchal cross]], a Latin cross with an additional horizontal bar, first appears in the 10th century. A wide variation of cross symbols is introduced for the purposes of [[Crosses in heraldry|heraldry]] beginning in the age of the [[Crusades]].<ref>William Wood Seymour, [https://archive.org/stream/crossintraditi00seym#page/360/mode/2up "The Cross in Heraldry"],  ''The Cross in Tradition, History, and Art'' (1898).</ref>