According to a 2001 census 68.8% of the population were Protestants, which is the highest percentage of all Carinthian municipalities. Therefore the Four Evangelists parish church, erected in 1903, is the largest Protestant church building in mainly Catholic Carinthia. Furthermore Arriach's coat of arms depicts an Eucharistchalice and a Luther rose.
A smaller Catholic church dedicated to Sts. Philipp and Jakob from about 1200 stands nearby. Arriach also features several historic rustic log homes preserved in quite good condition.