Armagh is a large settlement in Northern Ireland, and the county town of County Armagh. It is a site of historical importance for both Celtic paganism and Christianity and is the seat, for both the Roman Catholic Church and the Church of Ireland, of the Archbishop of Armagh.  Although classed as a medium-sized town, Armagh was granted city status by Queen Elizabeth II in 1994. Its population of 14,590 (2001 Census) makes it the least-populated city in both Northern Ireland and on the island of Ireland and the fourth smallest in the United Kingdom.

Eamhain Mhacha (or Navan Fort) at the city's edge, is believed to have been used as an ancient pagan ritual or ceremonial site. According to Irish mythology it was once the capital of Ulster, until it was abandoned during the 1st century. The site was named after the goddess Macha, and as the settlement grew on the hills nearby, it was also named after the goddess — Ard Mhacha means "Macha's height". This name was later anglicised as Ardmagh which eventually became Armagh.

When Christianity spread to Ireland during the mid-400s, Armagh became the island's "ecclesiastical capital", as Saint Patrick established his principal church there. Saint Patrick decreed that only those educated in Armagh could spread the gospel. According to the Annals of the Four Masters, in the year 457.

In 839 and 869, the monastery in Armagh was raided by Vikings. As with similar raids, their objective was simply to acquire valuables such as silver, which the churches and monasteries often kept. The Book of Armagh came from the monastery. It is a 9th century Irish manuscript now held by the Library of Trinity College, Dublin. It contains some of the oldest surviving specimens of Old Irish.

Armagh has been an educational centre since the time of Saint Patrick, and thus it has been referred to as "the city of saints and scholars". The educational tradition continued with the foundation of the Royal School in 1608 and the Armagh Observatory in 1790. This was part of the Archbishop's plan to have a university founded in the city. This ambition was finally fulfilled, albeit briefly, in the 1990s when Queen's University of Belfast opened an outreach centre in the former hospital building.

Armagh is the site of two cathedrals, both on hills and both named after Saint Patrick. The Church of Ireland cathedral dates back to around 445. The present-day, post-Reformation, Roman Catholic cathedral was constructed during the latter half of the 1800s and features twin 64m spires, making it the tallest such structure in the county. Armagh is the only city in the world which is home to two cathedrals of the same name.

The city is home to the Armagh Observatory, founded in 1790, and to the Armagh Planetarium, established in 1968 to complement the research work of the Observatory. The palace of the Archbishop of Armagh is now the local council offices and, along with the archbishop's private chapel, is open to the public. The Palace Stables heritage centre is a reconstructed stable block dating from the 1700s, which was once part of the Archbishop's estate.