Bagan (Burmese: ပုဂံ - Formerly: Pagan) is an ancient city and a UNESCO World Heritage Site in the Mandalay Region of Myanmar.

From the 9th to 13th centuries, the city was the capital of the Bagan Kingdom, the first kingdom that unified the regions that would later constitute Myanmar. During the kingdom's height between the 11th and 13th centuries, more than 10,000 Buddhist temples, pagodas, and monasteries were constructed in the Bagan plains alone, of which the remains of over 2200 temples and pagodas survive.

Bagan is the present-day standard Burmese pronunciation of the Burmese word Pugan (ပုဂံ), derived from Old Burmese Pukam (ပုကမ်). Its classical Pali name is Arimaddanapura (အရိမဒ္ဒနာပူရ, "the City that Tramples on Enemies"). Its other names in Pali are in reference to its extreme dry zone climate: Tattadesa (တတ္တဒေသ, "parched land"), and Tampadīpa (တမ္ပဒီပ, "bronzed country").

The Burmese chronicles also report other classical names of Thiri Pyissaya (သီရိပစ္စယာ; Pali: Siripaccaya) and Tampawaddy (တမ္ပဝတီ; Pali: Tampavatī).

Bagan stands out for not only the sheer number of religious edifices of Myanmar but also the magnificent architecture of the buildings, and their contribution to Burmese temple design. The artistry of the architecture of pagodas in Bagan proves the achievement of Myanmar craftsmen in handicrafts. The Bagan temple falls into one of two broad categories: the stupa-style solid temple and the gu-style (ဂူ) hollow temple.

According to the Burmese chronicles, Bagan was founded in the second century AD, and fortified in 849 AD by King Pyinbya, 34th successor of the founder of early Bagan. Mainstream scholarship however holds that Bagan was founded in the mid-to-late 9th century by the Mranma (Burmans), who had recently entered the Irrawaddy valley from the Nanzhao Kingdom.

It was among several competing Pyu city-states until the late 10th century when the Burman settlement grew in authority and grandeur.

From 1044 to 1287, Bagan was the capital as well as the political, economic, and cultural nerve center of the Bagan Empire. Over the course of 250 years, Bagan's rulers and their wealthy subjects constructed over 10,000 religious monuments (approximately 1000 stupas, 10,000 small temples and 3000 monasteries) in an area of 104 square kilometers (40 sq mi) in the Bagan plains.

The prosperous city grew in size and grandeur and became a cosmopolitan center for religious and secular studies, specializing in Pali scholarship in grammar and philosophical-psychological (abhidhamma) studies as well as works in a variety of languages on prosody, phonology, grammar, astrology, alchemy, medicine, and legal studies. The city attracted monks and students from as far as India, Sri Lanka and the Khmer Empire.

The culture of Bagan was dominated by religion. The religion of Bagan was fluid, syncretic and by later standards, unorthodox. It was largely a continuation of religious trends in the Pyu era where royal patronage of Theravada Buddhism co-existed with Mahayana Buddhism, Tantric Buddhism, various Hindu as well as native animist (nat) traditions.

The Pagan Empire collapsed in 1287 due to repeated Mongol invasions (1277–1301) and other factors. The city, once home to some 50,000 to 200,000 people, had been reduced to a small town, never to regain its preeminence. The city formally ceased to be the capital of Burma in December 1297 when the Myinsaing Kingdom became the new power in Upper Burma.

Bagan survived into the 15th century a human settlement, and as a pilgrimage destination throughout the imperial period. A smaller number of "new and impressive" religious monuments still went up to the mid-15th century but afterward, new temple constructions slowed to a trickle with fewer than 200 temples built between the 15th and 20th centuries.

The old capital remained a pilgrimage destination, but pilgrimage was focused only on most prominent temples out of the thousands such as the Ananda, the Shwezigon, the Sulamani, the Htilominlo, the Dhammayazika, and a few other temples along an ancient road.

Bagan, located in an active earthquake zone, had suffered from many earthquakes over the ages, with over 400 recorded earthquakes between 1904 and 1975. A major earthquake occurred on 8 July 1975 and damaged many temples, some severely and irreparably.

On 24 August 2016, another major earthquake hit central Myanmar and again inflicted major damage in Bagan; this time almost 400 temples were destroyed.

Today, 2229 temples and pagodas remain.

On 6 July 2019, Bagan was officially inscribed as a World Heritage Site by UNESCO, after 24 years since the military government first nominated the city in 1995, during the 43rd session of the World Heritage Committee.

This makes Bagan the second World Heritage Site in Myanmar, after the Ancient Cities of Pyu.