Over thousands of years, winter solstice celebrations evolved from pagan Roman Saturnalia festivals into Christmas. In the 4th century AD, the Roman Catholic Church designated December 25th as Jesus's birthday, transforming Saturnalia into a Christian holiday. In the Middle Ages, Christmas traditions spread across Europe. In the 1800s, American writers and illustrators popularized the character of Santa Claus, and during the 1920s, advertisers standardized the modern image of Santa. By the 1950s, Christmas had become a major commercial holiday focused on family, gift-giving, decorating, and feasting.