In hoc signo vinces
In hoc signo vinces (Classical Latin: [ɪn hoːk ˈsɪŋnoː ˈwɪnkeːs]; Ecclesiastical Latin: [in ok ˈsiɲɲo ˈvintʃes]) is a Latin phrase meaning "In this sign you will conquer." It is a translation, or rendering, of the Greek phrase "ἐν τούτῳ νίκα" en toútōi níka (Ancient Greek: [en tóːtɔ͜ːi níkaː]), literally meaning "in this, conquer".
Lucius Caecilius Firmianus Lactantius was an early Christian author (c. 240 – c. 320) who became an advisor to the first Christian Roman emperor, Constantine I, guiding his religious policy as it developed, and tutor to his son. His work De Mortibus Persecutorum has an apologetic character, but has been treated as a work of history by Christian writers. Here Lactantius preserves the story of Constantine's vision of the Chi Rho before his conversion to Christianity. The full text is found in only one manuscript, which bears the title, Lucii Caecilii liber ad Donatum Confessorem de Mortibus Persecutorum.
The historian bishop Eusebius of Caesaria states that Constantine was marching with his army (Eusebius does not specify the actual location of the event, but it is clearly not in the camp at Rome), when he looked up to the sun and saw a cross of light above it, and with it the Greek words "(ἐν) τούτῳ νίκα" ("In this, conquer"), a phrase often rendered into Latin as in hoc signo vinces ("in this sign, you will conquer").
At first, Constantine did not know the meaning of the apparition, but on the following night, he had a dream in which Christ explained to him that he should use the sign of the cross against his enemies. Eusebius then continues to describe the Labarum, the military standard used by Constantine in his later wars against Licinius, showing the Chi-Rho sign. The accounts by Lactantius and Eusebius, though not entirely consistent, have been connected to the Battle of the Milvian Bridge, having merged into a popular notion of Constantine seeing the Chi-Rho sign on the evening before the battle.
The phrase appears prominently placed as a motto on a ribbon unfurled with a passion cross to its left, beneath a window over the Scala Regia, adjacent to the equestrian statue of Emperor Constantine, in the Vatican. Emperors and other monarchs, having paid respects to the Pope, descended the Scala Regia, and would observe the light shining down through the window, with the motto, reminiscent of Constantine's vision, and be reminded to follow the Cross. They would thence turn right into the atrium of St. Peter's Basilica, ostensibly so inspired.
- Inscribed on the banner of the Sanfedismo in 1799
- Inscribed in Greek on the flag (obverse side) of the Sacred Band of the Greek War of Independence
- Inscribed in Greek on the coat of arms, insignia and flag of the 22nd Tank Brigade (XXII ΤΘΤ) of the Greek Army
- Motto of Holy Cross College, Kalutara, Sri Lanka
- Motto of Quitman High School, Quitman, Louisiana USA
- Motto of Instituto Tecnológico de Mérida, Mérida, Mexico
- Motto of Holy Cross College, Arima, Trinidad
- Motto of Holy Cross School, Winnipeg, Manitoba, Canada.
- Motto of Georgian Institute of Public Affairs, Tbilisi, Georgia
- Motto of Wah Yan College, Wan Chai, Hong Kong
- Motto of Wah Yan College, Yau Ma Tei, Hong Kong
- Motto of the College of the Holy Cross, Worcester, MA 
- Is the motto on the coat of arms of the city of Plzeň, Czech Republic.
- The phrase is in the coat of arms of the city of Birkirkara, the largest city on the island of Malta, and the city of Bayamon, Puerto Rico.
- Public motto of the Sigma Chi undergraduate fraternity.
- It has been used in some versions of logo for the brand of cigarettes, Pall Mall.
- "Lucius Caecilius Firmianus Lactantius". Online Catholic Encyclopedia. New Advent.
- Roberts, Alexander; Donaldson, James, eds. (1871). "The manner in which persecutors died. Chapter 44". The works of Lactantius. Volume II. Ante-Nicene Christian Library: Translations of the writings of the Fathers. Down to A.D. 325 XXII. Edinburgh. p. 203.
- Eusebius. "1.28". Vita Constantini. www.documentacatholicaomnia.eu. p. 944.
- Haaren, John H.; Poland, A. B. (2006) . Famous Men of Rome. Yesterday's Classics. p. 229. ISBN 978-159915-046-8.
- Eusebius, Vita Constantini 1.31, p. 946.
- Chadwick, Owen. 1981. The Popes and European Revolution. Oxford University Press. ISBN 0-19-826919-6. p. 474.
- Helene P. Kokkone, Katerina Korre-Zographou, Chrysa Daskalopoulou (1997). Ελληνικές Σημαίες, Σήματα, Εμβλήματα (in Greek). Athens: G. Tsiberiotes. ISBN 960-7795-01-6.
- "Εμβλήματα: XXII ΤΘΤ" (in Greek). Hellenic Army General Staff.
- "College Seal". College of the Holy Cross. Retrieved 25 March 2014.
- "Story of Coat of Arms". 24 November 2010. Retrieved 4 January 2012.
- "Sigma Chi Crest".
- Pall Mall Example
- Chris Harrald et al. The Cigarette Book: The History and Culture of Smoking
- Grierson, Philip (1982). Byzantine Coins. University of California Press. p. 111. ISBN 0-520-04897-0.
- Eusebius. "1.28". Βίος Κωνσταντίνου [Vita Constantini] (in Greek). At the Internet Archive.
- Eusebius. "1.28". Eusebius - Constantine and the sign of the cross. www.earlychurchtexts.com (in Greek). Passages 1.26-31 of Vita Constantini.
- Eusebius. "1.28". Vita Constantini. www.documentacatholicaomnia.eu (in Latin). Book 1. p. 7 (21–22 on scanned book).
- Lactantius. "Lucii Caecilii liber ad Donatum Confessorem de Mortibus Persecutorum". www.thelatinlibrary.com (in Latin).