This is What the Cross Looked Like According to Early Christian Writers

Too tired to explain right now but a colleague has demonstrated the pertinent Patristic references:

Justin Martyr, Dialogue with Trypho 91 "Now, no one could say or prove that the horns of an unicorn represent any other fact or figure than the type which portrays the cross. For the one beam is placed upright, from which the highest extremity is raised up into a horn, when the other beam is fitted on to it, and the ends appear on both sides as horns joined on to the one horn. And the part which is fixed in the centre, on which are suspended [1] those who are crucified, also stands out like a horn; and it also looks like a horn conjoined [2] and fixed with the other horns. 

Irenaeus, Against Heresies 2.24.4 "The very form of the cross, too, has five extremities [3], two in length, two in breadth, and one in the middle, on which [last] the person rests who is fixed by the nails."

Tertullian, Ad Nationes 12.3,4 "Every piece of timber which is fixed in the ground in an erect position is a part of a cross, and indeed the greater portion of its mass. But an entire cross is attributed to us, with its transverse beam, of course, and its projecting seat."[4] 

Tertullian, An Answer to the Jews 10.2.7,8 "Of course no one-horned rhinoceros was there pointed to, nor any two-horned minotaur. But Christ was therein signified: “bull,” by reason of each of His two characters—to some fierce, as Judge; to others gentle, as Saviour; whose “horns” were to be the extremities of the cross. For even in a ship's yard— which is part of a cross— this is the name by which the extremities are called; while the central pole of the mast is a “unicorn.”[5] 

Tertullian, Against Marcion 3.18.3,4 "For of the antenna, which is a part of a cross, the ends are called horns; while the midway stake of the whole frame is the unicorn."[6] 

Clement Instructor 1.5 We, then, who are infants, no longer roll on the ground, nor creep on the earth like serpents as before, crawling with the whole body about senseless lusts; but, stretching upwards in soul, loosed from the world and our sins, touching the earth on tiptoe so as to appear to be in the world, we pursue holy wisdom, although this seems folly to those whose wits are whetted for wickedness.

Clement  "Rightly, then, are those called children who know Him who is God alone as their Father, who are simple, and infants, and guileless, who are lovers of the horns of the unicorns. 

Clement (in an unknown work cited in Parable of the Prodigal Son, Luke xv., Oration on Luke xv., towards the close) "To the sons, then, who come to Him, the Father gives the calf, and it is slain and eaten. But those who do not come to Him He pursues and disinherits, and is found to be a most powerful bull. Here, by reason of His size and prowess, it is said of Him, “His glory is as that of an unicorn.” [Numb. xxiii. 22] And the prophet Habakkuk sees Him bearing horns, and celebrates His defensive attitude—“horns in His hands.” [Hab. iii. 4]. Wherefore the sign shows His power and authority,—horns that pierce on both sides, or rather, on all sides, and through everything. And those who eat are so strengthened, and retain such strength from the life-giving food in them, that they themselves are stronger than their enemies, and are all but armed with the horns of a bull; as it is said, “In thee shall we butt our enemies.”

[1] Greek εποχουνται "they ride" which is 3rd plural pres ind middle of ἐποχέομαι "I ride" which is 1st singular pres ind middle of ἐποχεύω "I spring upon, cover, copulate." 

[2]Greek συνεσχηματισμένον "having been shaped into a certain form in conformance with" 

[3] fines et summitates = ends and high points 

[4] illo sedilis excessu = that / the well-known projection / excess / towering above / deviation / transgression of a seat

[5] unicornis autem medio stipite palus = "but the pale from the middle of the post is singlehorned." The quote above this is one the worst translations of Latin I have ever seen! 

[6] unicornis autem medius stipitus palus = "the middle pale of the post is singlehorned." Again, in the quote is an extremely poor translation of the Latin. But good enough to fool a lot of people!