While the birth year of Jesus is estimated among modern historians to have been between 7 and 2 BC, the exact month and day of his birth are unknown.[16][17] His birth is mentioned in two of the four canonical gospels. By the early-to-mid 4th century, the Western Christian Church had placed Christmas on December 25,[18] a date later adopted in the East,[19][20] although some churches celebrate on the December 25 of the older Julian calendar, which corresponds to January in the modern-day Gregorian calendar. The date of Christmas may have initially been chosen to correspond with the day exactly nine months after early Christians believed Jesus to have been conceived,[21] or with one or more ancient polytheistic festivals that occurred near southern solstice (i.e., the Roman winter solstice); a further solar connection has been suggested because of a biblical verse[a] identifying Jesus as the "Sun of righteousness".