Ani (Armenian: Անի; Ancient Greek: Ἄνιον, romanized: Ánion; Latin: Abnicum) is a ruined medieval Armenian city now situated in Turkey's province of Kars, next to the closed border with Armenia.

Between 961 and 1045, it was the capital of the Bagratid Armenian kingdom that covered much of present-day Armenia and eastern Turkey. The iconic city was often referred to as the "City of 1,001 Churches," though the number was significantly less. To date, 50 churches, 33 cave chapels and 20 chapels have been excavated by archaeologists and historians. Ani stood on various trade routes and its many religious buildings, palaces, and sophisticated fortifications distinguished it from other contemporary urban centers in the Armenian kingdom. Among its most notable buildings was the Cathedral of Ani, which is associated with early examples of Gothic architecture and that scholars argue influenced the great cathedrals of Europe in the early gothic and Romanesque styles; its ribbed vaulting would not be seen in European cathedrals for at least another two centuries. At its height, Ani was one of the world's largest cities, with a population of well over 100,000, though this seems highly optimistic given its limited area.

Renowned for its splendor, Ani was sacked by the Mongols in 1236. Ani never recovered from a devastating 1319 earthquake and, more significantly, from the shifting of regional trade routes, and was abandoned by the 17th century. Ani is a widely recognized cultural, religious, and national heritage symbol for Armenians. According to Razmik Panossian, Ani is one of the most visible and ‘tangible’ symbols of past Armenian greatness and hence a source of pride. In 2016, it was added onto the UNESCO World Heritage List. After two decades of continuous international efforts, Ani Archaeological Site has transformed from a seat of conflict and geopolitical instability to a center of cultural tourism that might foster cultural exchange and deepening historical understanding.

The city took its name from the Armenian fortress-city and pre-Christian religious center of Ani-Kamakh located in the region of Daranaghi in Upper Armenia. Ani was also previously known as Khnamk, although historians are uncertain as to why it was called so; according to philologist and Armenologist Heinrich Hübschmann, this name has nothing to do with the ordinary Armenian verb khnamel ("to care for"). According to the second edition of the Encyclopedia of Islam: "A suggestion has been made that the town may owe its name to a temple of the Iranian goddess Anāhita (the Greek Anaďtis)". The Turkish government previously attempted to obscure the name of the town as Anı in order to give it a "more Turkish character".

The city is located on a triangular site, visually dramatic and naturally defensive, protected on its eastern side by the ravine of the Akhurian River and on its western side by the Bostanlar, or Tsaghkotsadzor, valley. The Akhurian is a branch of the Araks River and forms part of the currently closed border between Turkey and Armenia. The site is at an elevation of around 1,340 meters (4,400 ft).

The site is located in the Turkish province of Kars. Kars is currently an important center for local livestock trades and cheese production. It is linked by railroad with many important Turkish cities and is also considered to be an important military site due to its positioning near Turkey's border with Armenia. Ani is about 400 m (1,300 ft) from the Turkey-Armenia border. Across the border is the Armenian village of Kharkov, part of Shirak Province.

Armenian chroniclers such as Yeghishe and Ghazar Parpetsi first mentioned Ani in the 5th century. They described it as a strong fortress built on a hilltop and a possession of the Armenian Kamsarakan dynasty.

By the early 9th century, the former territories of the Kamsarakans in Arsharunik and Shirak (including Ani) had been incorporated into the territories of the Armenian Bagratuni dynasty. The Bagratuni dynasty was the second notable dynasty in the Armenian kingdom. They secured their independence from the Arabs near the end of the 9th century after being controlled by the Persians and Umayyad Arabs for many years at this point. The king of Bagratid Armenia that led to this independence was Ashot I. He had a short-lived position as the king of the Bagratid dynasty, however, the impact of securing the freedom of the dynasty would last for many years. His son, Smbat I, ruled directly after he did. The Bagratid dynasty consisted of many sub-kingdoms, the most notable of which were the Kingdom of Kars, Lori, Syunik, Artsakh, and Vaspurakan.

The Bagratuni dynasty led to some of the most notable works of art and architecture in Armenia's history, one of which being the Cathedral of Ani. The leader of the Bagratid dynasty, Ashot Msaker (Ashot the Meateater) (806–827) was given the title of ishkhan (prince) of Armenia by the Caliphate in 804. The Bagratunis had their first capital at Bagaran, some 40 km (25 mi) south of Ani, before moving it to Shirakavan, some 25 km (16 mi) northeast of Ani, and then transferring it to Kars in the year 929. In 961, king Ashot III (953–77) transferred the capital from Kars to Ani. Ani expanded rapidly during the reign of King Smbat II (977–89). In 992 the Armenian Catholicosate moved its seat to Ani. In the 10th century the population was perhaps 50,000–100,000. By the start of the eleventh century the population of Ani was well over 100,000, and its renown was such that it was known as the "city of forty gates" and the "city of a thousand and one churches." Ani also became the site of the royal mausoleum of Bagratuni kings.

Ani attained the peak of its power during the long reign of King Gagik I (989–1020). After his death his two sons quarreled over the succession. The eldest son, Hovhannes-Smbat (1020–41), gained control of Ani while his younger brother, Ashot IV (1020–40), controlled other parts of the Bagratuni kingdom. Hovhannes-Smbat, fearing that the Byzantine Empire would attack his now-weakened kingdom, made the Byzantine Emperor Basil II his heir. When Hovhannes-Smbat died in 1041, Emperor Michael IV the Paphlagonian, claimed sovereignty over Ani. The new king of Ani, Gagik II (1042–45), opposed this and several Byzantine armies sent to capture Ani were repulsed. However, in 1046 Ani surrendered to the Byzantines, after Gagik was invited to Constantinople and detained there, and at the instigation of pro-Byzantine elements among its population. A Byzantine governor was installed in the city.

Ani lied along any previously important trade routes, but because of its size, power, and wealth it became an important trading hub. Its primary trading partners were the Byzantine Empire, the Persian Empire, the Arabs, as well as smaller nations in southern Russia and Central Asia.

In 1064, a large Seljuk army under Alp Arslan attacked Ani; after a siege of 25 days, they captured the city and slaughtered its population. An account of the sack and massacres in Ani is given by the Turkish historian Sibt ibn al-Jawzi, who quotes an eyewitness saying:

The army entered the city, massacred its inhabitants, pillaged and burned it, leaving it in ruins and taking prisoner all those who remained alive...The dead bodies were so many that they blocked the streets; one could not go anywhere without stepping over them. And the number of prisoners was not less than 50,000 souls. I was determined to enter the city and see the destruction with my own eyes. I tried to find a street in which I would not have to walk over the corpses; but that was impossible.

In 1072, the Seljuks sold Ani to the Shaddadids, a Muslim Kurdish dynasty. The Shaddadids generally pursued a conciliatory policy towards the city's overwhelmingly Armenian and Christian population and married several members of the Bagratid nobility. Whenever the Shaddadid governance became too intolerant, however, the population would appeal to the Christian Kingdom of Georgia for help. The Georgians captured Ani five times between 1124 and 1209: in 1124, 1161, 1174, 1199. The first three times, it was recaptured by the Shaddadids.

In the year 1199, Georgia's Queen Tamar captured Ani and in 1201 gave the governorship of the city to the generals Zakare and Ivane. Zakare was succeeded by his son Shanshe (Shahnshah). Zakare's new dynasty — the Zakarids — considered themselves to be the successors to the Bagratids. Prosperity quickly returned to Ani; its defences were strengthened and many new churches were constructed.

In 1217 and 1220, the city came under attack from the Seljuk Sultanate of Rum whose forces destroyed and pillaged the city however they did not occupy it.

The Mongols unsuccessfully besieged Ani in 1226, but in 1236 they captured and sacked the city, massacring large numbers of its population. During Mongol invasion of Georgia in 1238-39 Queen Rusudan had to evacuate Tbilisi for Kutaisi, leaving eastern Georgia in the hands of atabeg Avag Zakarian, Shahnshah Zakarian, and Kakhetian lord, Egarslan Bakurtsikheli. The Mongol general Toghta was sent by Chaghatai to assault Avag's troops at the fortress of Kayan. After some resistance, Avag surrendered, and has to agree to pay tribute to the Mongols, and to provide let his troops join the Mongol army. The combined troops went on to Ani, the Armenian capital being defended by Shahnshah Zakarian, but the city was eventually captured and destroyed. Following this disastrous campaign of 1238–1239, the Armenians and Georgians made peace with the Mongols and agreed to pay them tribute and supply their troops (Georgian–Mongolian treaty of 1239).

Following the decline of the Il-Khanate, during the later part of the reign of George V (between 1319 and 1335) and the reign of the later king Bagrat V, the city of Ani again became part of the Kingdom of Georgia.

By the end of the 14th century, the city was ruled by a succession of local Turkish dynasties, including the Jalayrids and the Kara Koyunlu (Black Sheep clan) who made Ani their capital. It was ruined by an earthquake in 1319. Tamerlane captured Ani in the 1380s. On his death the Kara Koyunlu regained control but transferred their capital to Yerevan. In 1441 the Armenian Catholicosate did the same. The Persian Safavids then ruled Ani until it became part of the Turkish Ottoman Empire in 1579. A small town remained within its walls at least until the middle of the seventeenth century, but the site was entirely abandoned by 1735 when the last monks left the monastery in the Virgin's Fortress or Kizkale.

In the first half of the 19th century, European travelers discovered Ani for the outside world, publishing their descriptions in academic journals and travel accounts. The private buildings were little more than heaps of stones but grand public buildings and the city's double wall were preserved and reckoned to present "many points of great architectural beauty". Ohannes Kurkdjian produced a stereoscopic image of Ani in the second half of the 19th century.

In 1878, the Ottoman Empire's Kars region—including Ani—was incorporated into the Russian Empire's Transcaucasian region. In 1892 the first archaeological excavations were conducted at Ani, sponsored by the St. Petersburg Academy of Sciences and supervised by the Georgian archaeologist and orientalist Nicholas Marr (1864–1934). Marr's excavations at Ani resumed in 1904 and continued yearly until 1917. Large sectors of the city were professionally excavated, numerous buildings were uncovered and measured, the finds were studied and published in academic journals, guidebooks for the monuments and the museum were written, and the whole site was surveyed for the first time. Emergency repairs were also undertaken on those buildings that were most at risk of collapse. A museum was established to house the tens of thousands of items found during the excavations. This museum was housed in two buildings: the Minuchihr mosque, and a purpose-built stone building. Armenians from neighboring villages and towns also began to visit the city on a regular basis, and there was even talk by Marr's team of building a school for educating the local Armenian children, building parks, and planting trees to beautify the site.

In 1918, during the latter stages of World War I, the armies of the Ottoman Empire were fighting their way across the territory of the newly declared Republic of Armenia, capturing Kars in April 1918. At Ani, attempts were made to evacuate the artifacts contained in the museum as Turkish soldiers were approaching the site. About 6,000 of the most portable items were removed by archaeologist Ashkharbek Kalantar, a participant of Marr's excavation campaigns. At the behest of Joseph Orbeli, the saved items were consolidated into a museum collection; they are currently part of the collection of Yerevan's State Museum of Armenian History. Everything that was left behind was later looted or destroyed. Turkey's surrender at the end of World War I led to the restoration of Ani to Armenian control, but a resumed offensive against the Armenian Republic in 1920 by Mustafa Kemal Atatürk resulted in Turkey's recapture of Ani. In 1921 the signing of the Treaty of Kars formalized the incorporation of the territory containing Ani into the Republic of Turkey.

In May 1921, the government minister Rıza Nur ordered the commander of the Eastern Front, Kazım Karabekir, for the monuments of Ani to "be wiped off the face of the earth." Karabekir records in his memoirs that he has vigorously rejected this command and never carried it out. Some destruction did take place, including most of Marr's excavations and building repairs. In October of the same year, a separate treaty was signed between Turkey and the RSFSR, confirming the border between Turkey and the soviet republic of Armenia as it is today. The Russian negotiator Ganeckij of this treaty tried to include Ani into the soviet republic of Armenia, but Karabekir did not agree.

During the Cold War, Ani lay on the Turkish-Soviet border, a segment of the Iron Curtain. In the 1950s Ani was part of the USSR's territorial claims on Turkey. In 1968 there were negotiations between the Soviet Union and Turkey, in which Ani would be transferred to Soviet Armenia in exchange for two Kurdish villages being transferred to Turkey, however nothing resulted from the talks.

During the Cold War, and until 2004, a permit from the Turkish Ministry of Culture was required. At one point in the 1980s, photography was banned, as the site lay on the then Turkish-Soviet border.

Today, according to Lonely Planet and Frommer's travel guides to Turkey:

Official permission to visit Ani is no longer needed. Just go to Ani and buy a ticket. If you don't have your own car, haggle with a taxi or minibus driver in Kars for the round-trip to Ani, perhaps sharing the cost with other travelers. If you have trouble, the Tourist Office may help. Plan to spend at least a half-day at Ani. It's not a bad idea to bring a picnic lunch and a water bottle.

From the Armenian side of the border, in Shirak Province, an observation post has been set up near the village of Haykadzor, complete with an information panel, but the view is very poor. The outpost of Kharkov offers an excellent view, but access is restricted by border troops and Russian military personnel. Permission to visit is granted at the Ministry of Foreign Affairs in Yerevan for free and takes one week.

According to The Economist, Armenians have "accused the Turks of neglecting the place in a spirit of chauvinism. The Turks retort that Ani's remains have been shaken by blasts from a quarry on the Armenian side of the border."

Another commentator said: Ani is now a ghost city, uninhabited for over three centuries and marooned inside a Turkish military zone on Turkey's decaying closed border with the modern Republic of Armenia. Ani's recent history has been one of continuous and always increasing destruction. Neglect, earthquakes, cultural cleansing, vandalism, quarrying, amateurish restorations and excavations – all these and more have taken a heavy toll on Ani's monuments.

In the estimation of the Landmarks Foundation (a non-profit organization established for the protection of sacred sites) this ancient city "needs to be protected regardless of whose jurisdiction it falls under. Earthquakes in 1319, 1832, and 1988, all have had devastating effects on the architecture of the city. The city of Ani is a sacred place which needs ongoing protection."

In an October 2010 report titled Saving Our Vanishing Heritage, Global Heritage Fund identified Ani as one of 12 worldwide sites most "On the Verge" of irreparable loss and destruction, citing insufficient management and looting as primary causes.

The World Monuments Fund (WMF) placed Ani on its 1996, 1998, and 2000 Watch Lists of 100 Most Endangered Sites. In May 2011, WMF announced it was beginning conservation work on the cathedral and Church of the Holy Redeemer in partnership with the Turkish Ministry of Culture. In 2023, with the support of the WMF and the Calouste Gulbenkian Foundation, Anadolu Kültür brought together experts from worldwide to launch a mobile application which allows virtual exploration of Ani.

In March 2015, it was reported that Turkey will nominate Ani to be listed as a UNESCO World Heritage Site in 2016. The archaeological site of Ani was inscribed as a UNESCO World Heritage Site on July 15, 2016. According to art historian Heghnar Zeitlian Watenpaugh the addition "would secure significant benefits in protection, research expertise, and funding." It gained this status due to its amazing representation of medieval Armenian architecture, however, there were three main criteria that further explain why this aspect of Ani is significant. The first of these criteria is that "Ani was a meeting place for Armenian, Georgian, and diverse Islamic cultural traditions that were reflected in the architectural design, material, and decorative details of the monuments". Ani's location on the silk road brought in many visitors from various parts of the world, these visitors brought with them new cultures and architectural styles. This unique combination of residents in the city led many of the buildings in Ani to have a never-before-seen architectural style that is distinct to this region of the world.

This new style, formed when Ani was at its prime, still has a large impact on the current architecture in its region. The second criterion that caused Ani to gain the status of "outstanding universal value" from UNESCO is the fact that "Ani bears exceptional testimony to Armenian cultural, artistic, architectural, and urban design development and it is an extremely extraordinary representation of Armenian religious architecture known as the 'Ani school', reflecting its techniques, style, and material characteristics". Ani's architecture is an important reminder to the citizens of Armenia of their past. Its buildings have beautiful stone working and architectural designs that were very ahead of their time, this is a major source of pride for the Armenian people. The third criterion that gained Ani the right to be protected is that "Ani offers a wide panorama of medieval architectural development thanks to the presence at the site of almost all the architectural types that emerged in the region in the course of six centuries from 7th to 13th centuries AD". This is due to the cities "military, religious, and civil buildings". UNESCO states that Ani "is also considered a rare settlement", this is because many different styles of Armenian churches can be seen throughout the city, the styles of these churches were developed between the 4th and 8th century AD.

Ani is currently classified by UNESCO as a 1st degree archaeological conservation site. This range of protection is continually being enlarged by UNESCO, however, as even Ani's surrounding areas are classified as 3rd-degree archaeological conservation sites. The Ministry of Culture and Tourism is the main organization in charge of the conservation of Ani, however, the General Directorate of Cultural Heritage and Museums also participates in helping with tasks such as restoration. There are also some other local branches in charge of some of the conservation efforts.

When inscribing Ani Archaeological Site on the UNESCO World Heritage List, the 40th Session of the World Heritage Committee Member States highlighted: "…...the cosmopolitan setting of medieval Ani is a potential model for the improvement of the contemporary international relations in the region, starting from the involvement of the international community in the efforts to preserve this exceptional multi-cultural archaeological site."

All the structures at Ani are constructed using the local volcanic basalt, a sort of tufa stone. It is easily carved and comes in a variety of vibrant colors, from creamy yellow, to rose-red, to jet black. It is important to note that throughout the attacks and natural disasters Ani has faced throughout the years, all of the buildings have at least significant structural damages, or have otherwise been completely destroyed. The most important surviving monuments are as follows.