The crux simplex is an instrument of torture and execution recognized by modern authors as one of the types of crosses that existed in the ancient world. In the sixteenth century the scholar Justus Lipsius (1547–1606) qualified itself in his book De cruce libri tres. Most recently as archaeologists and historians like Joe Zias, (Antiquities Museum Jerusalem) and Frederick T. Zugibe have recognized that the crux simplex, consisting of only a vertical beam without crossbar, "in fact is a kind of crucifixion". This type of cross"was the easiest available way to torture and kill criminals". Indeed it isthe most common form of crosses used by the Persians, Assyrians, Seleucids and Phoenicians.
Patrick Farbairn, in The Imperial Bible Dictionary states that "even among the Romans the crux (from which our cross is derived) appears to have originally been a stick upright, and this always remained the more prominent part".  Josephus wrote in The Jewish War: "the soldiers out of rage and hatred, had fun nailing their prisoners in different postures". By implication the word crux took the metaphorical meaning of severe torment.
The Crucifixion Before Rome
Crucifixion probably originated with the Assyrians and Babylonians. The Assyrians impaled his victims by the ribs and left them hanging spears or high stakes.
Later this method of execution was adopted by the Persians who used it systematically during the sixth century BCE. On the Zoroastrian religion of Persia it was considered sacred to both the fireand the earth, so their funeral rites excluded burial or cremation, because of that the corpses only be placed in wooden beds supported by tall poles and the birds devour it. The same logic would apply to those sentenced to death tying them or hanging them high posts or fences as well not profane the sacred.
The Hebrew Bible (OT) testifies to this Persian Eastern practice, when it reads that Darius I the Great issued an order that no one interfere in rebuilding the temple in Jerusalem on pain of being set (literally, "elevation") on a tree ripped from your own home. During the reign of Ahasuerus (Xerxes I), the son of Darius, two of the guardians of the palace gate were hung or attached to a pole, the usual punishment Persians gave traitors. Haman and his ten sons were hungon a tree for similar reasons. The Greek historian Herodotus also cites other cases of application of such punishment by the Persians. The Dead Sea Scrolls, which are dated as of the first century, cited Deuteronomy 21:22-23 with reference to crucifixion practiced by the Romans and later Hasmoneans. For example, they applied this passage to executions by Alexander Jannaeus in the year 88 BCE. 
When Alexander the Great conquered the Persian Empire adopted, among other Oriental customs, the crucifixion, which cruelly applied after the conquest of the city of Tyre when he ordered the crucifixion of about 2000 people at sea.
Crucifixion in ancient Rome
The crucifixion was a death sentence widely used in ancient Rome, being excluded for Roman citizens. It was applied to the lower classes and slaves. Cicero called it the worst tortures. It is possible that in the Roman world the Carthaginian Phoenicians entered the crucifixion.
According doctor Frederick Zugibe this stile of vertical crucifixion precipitate choking soon, from hours to even minutes, depending on whether some support on the feet for had incorporated and breathe. The eastern Phoenician crucifixion had merged with the Roman custom of the rite of "patibullum" which was to make charging inmates a wooden yoke (furca, patibulum) to the place of execution.
Using the crux simplex by the Romans
However, some believe that the Romans continued to use the crux simplex method in exceptional cases. Referring to mass executions by the Romans Professor Herman Fulda wrote in 20th-century: "Trees were not everywhere available at the places chosen for public execution. So a simple beam was sunk into the ground. On this the outlaws, with hands raised upward and often also with their feet, were bound or nailed".
- Frederick T. Zugibe (2005). The Crucifixion of Jesus: A Forensic Inquiry. Rowman & Littlefield. p. 40-41. ISBN 9781590770702.
- T. Lewis, Charlton; Short, Charles, A Latin Dictionary. Harper and Brothers publishers. New York in 1879. Oxford University Press. 
- Joseph Twadell Shipley (2001). The Origins of English Words: A Discursive Dictionary of Indo-European Roots. JHU Press. p. 113. ISBN 9780801867842.
- Dizionario Etimologico Online (Italian)
- P. Fairbairn (1874). The Imperial Bible-Dictionary I. London. p. 376.
- "The Jewish War" 5:451-452)
- Christopher Francese (2007). Ancient Rome in So Many Words. Hippocrene Books. pp. 202–203. ISBN 9780781811538.
- Ezra 6:11
- Esther 2:21-23
- Esther 5:14
- Herodotus, Book III, 125, 159; IV, 43
- 11QT, Deut 64:6-13; 4QpNah, Deut 3-4:1:1-11
- Cf. Josephus' Antiquities of the Jews" 13.14.2. “The Jewish War” 1.4.5-6
- Curtius Rufus, Hist. Alex. 4.4.17.
- Hermann Fulda (1878). Das Kreuz und die Kreuzigung" (The cross and crucifixion). Breslau (Wroclaw). pp. 109, 219, 220.