christianity has been the largest religion by number of adherents since the early middle ages: it was introduced under the ancient romans, developing as celtic christianity. according to tradition, christianity arrived in the 1st or 2nd century. the most popular form is anglicanism (known as episcopalism in scotland). dating from the 16th-century reformation, it regards itself as both catholic and reformed. the head of the church is the monarch of the united kingdom, as the supreme governor. it has the status of established church in england. there are just over 26 million adherents to anglicanism in britain today, although only around one million regularly attend services. the second largest christian practice is the latin rite of the roman catholic church, which traces its history to the 6th century with augustine's mission and was the main religion for around a thousand years. there are over 5 million adherents today, 4.5 million in england and wales and 750,000 in scotland, although fewer than a million catholics regularly attend mass.