Historically, religion has been a prominent symbol of ethnic identity in the Horn of Africa. Christianity was established in the 4th century CE on the coast and appeared soon afterward in the plateau, where it was embraced by the Ethiopian highlanders. Prior to Eritrea’s secession from Ethiopia in 1993, about half the population of Eritrea belonged to the Ethiopian Orthodox Tewahedo Church, including nearly all the Tigrinya. After the country gained its independence, it appealed to the patriarch of the Coptic church for autocephaly, which was granted.
About one-half of Eritrea’s population is Christian, with members of the Eritrean Orthodox Tewahedo Church accounting for some two-fifths. The rest of the Christian population is primarily Roman Catholic with a small number of Protestants, stemming from the time of Italian colonial rule (1889–1941), when Roman Catholic and Protestant European missionaries introduced their own versions of Christianity into Eritrea. They had considerable success among the small Kunama group, and they also attracted a few townspeople with the offer of modern education.
Following the rise of Islam in Arabia in the 7th century, Muslim power flowed over the Red Sea coast, forcing the Ethiopians to retreat deep into their mountain fastness. Islam displaced other creeds in the lowlands of the Horn, and it remains the faith of about one-half of the Eritrean population, including nearly all the people inhabiting the eastern coast and the western plain of Eritrea, as well as the northernmost part of the plateau. Thus, while Islam claims nearly all the pastoralists, Christianity is dominant among the cultivators.