27 October, 312

27 October 312 Chi Rho Cross it was 27th October 312, the day before an important battle on Milvian Bridge in Rome, which he won. Since chi and rho form the monogram of Christ, he understood it was a sign from the Christian God and thenceforth Constantine became more tolerant of Christianity http://www.seiyaku.com/customs/crosses/chi-rho.html