According to Scripture, God commanded Moses to lead the Israelites out of Egypt by speaking to him from a bush which, although on fire, was unaffected by the flames. Empress Helena, the mother of Constantine the Great (272–337 AD), the first Roman emperor to convert to Christianity, built a church on the site of the Burning Bush in the 4th century AD. It was later rebuilt by Emperor Justinian I (527–565 AD), who included it within the much larger church that he built, the Church of the Transfiguration of Christ the Savior. A small altar on a marble floor marks the location of the Burning Bush, directly above its roots. A large bush, which used to be inside the church, thrives to this day, just on the other side of the wall behind the altar.