Armenian church tradition places the cathedral's foundation between 301 and 303. or archangel Sandaramet, major figures in Zoroastrian-influenced Armenian mythology.
In his History of the Armenians, Agathangelos narrates the legend of the cathedral's foundation. Armenia's patron saint Gregory the Illuminator had a divine vision descending from heaven and striking the earth with a golden hammer to show where the cathedral should be built. Later tradition associated the figure with Jesus Christ, hence the name of Etchmiadzin (էջ ēĵ "descent" + մի mi "only" + -ա- -a- (linking element) + ծին tsin "begotten"), which translates to "the Descent of the Only-Begotten "
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Malachia Ormanian suggested that the cathedral was built in 303 within seven months because the building was not huge and probably, partially made of wood. He also argued that the foundation of the preexisting temple could have been preserved. Vahagn Grigoryan dismisses these dates as implausible and states that at least several years were needed for its construction. He cites Agathangelos, who does not mention the cathedral in an episode that took place in 306 and suggests the usage of the span of 302 to 325—the reign of Gregory the Illuminator as Catholicos as the dates of the cathedral's construction.
Archaeological excavations in 1955–56 and 1959, led by Alexander Sahinian, uncovered the remains of the original fourth-century building, including two levels of pillar bases below the current ones and a narrower altar apse under the present one. Among them, Suren Yeremian and Armen Khatchatrian held that the original church had been in the form of a rectangle with a dome supported by four pillars. Stepan Mnatsakanian suggested that the original building had been a "canopy erected on a cross [plan]," while Vahagn Grigoryan proposes what Mnatsakanian describes as an "extreme view," that the cathedral has been essentially in the same form as it is today.
Reconstruction and decline
thumb|The ground plan of the cathedral after the 5th century reconstruction
The city of Vagharshapat and the cathedral were almost completely destroyed during the invasion of Sasanian King Shapur II . In 450, in an attempt to impose Zoroastrianism on Armenians, Sasanian King Yazdegerd II built a fire temple inside the cathedral. The pyre of the fire temple was unearthed under the altar of the east apse during the excavations in the 1950s. or 484, the cathedral never lost its significance and remained "one of the greatest shrines of the Armenian Church." The last known renovations until the 15th century were made by Catholicos Komitas in 618 (according to Sebeos) and Catholicos Nerses III (). In the poem, which tells about the consequences of the Mongol and Mamluk invasions of Armenia and Cilicia, Orbelian portrays Etchmiadzin Cathedral "as a woman in mourning, contemplating her former splendor and exhorting her children to return to their homeland [...] and restore its glory."
From revival to plunder
Following the fall of the Armenian Kingdom of Cilicia in 1375, the See of Sis experienced decline and disarray. The Catholicosate of Aghtamar and the locally influential Syunik bishops enhanced the importance of the region around Etchmiadzin. In 1441 a general council of several hundred religious figures met in Etchmiadzin and voted to reestablish a catholicosate there. The cathedral was restored by Catholicos Kirakos (Cyriacus) between 1441 and 1443. Etchmiadzin was plundered in 1604.
The Shah wanted to "dispel Armenian hopes of returning to their homeland" in order to provide Persia with a strong Armenian presence. He wanted to destroy the cathedral and have it physically transferred to the newly founded Armenian community of New Julfa near the royal capital of Isfahan. the Right Arm of Gregory the Illuminator—were moved to New Julfa. They were incorporated in the local Armenian St. Georg Church when it was built in 1611. Fifteen stones from Etchmiadzin still remain at St. Georg.
thumb|An engraving of Etchmiadzin in the late 17th century by [[Jean Chardin (from 1811 edition)․]]
17th–18th centuries
Since 1627, the cathedral underwent a major renovation under Catholicos Movses (Moses), when the dome, ceiling, roof, foundations and paving were repaired. At this time, cells for monks, a guesthouse and other structures were built around the cathedral.<br />From left to right: Hripsime, Gayane, Etchmiadzin Cathedral, and Shoghakat. ]]
thumb|Painting of the cathedral by an unknown European artist (1870s)
Russian takeover
The Russian Empire gradually penetrated Transcaucasia by the early 19th century. Persia's Erivan Khanate, in which Etchmiadzin was located, became an important target for the Russians. In June 1804, during the Russo-Persian War (1804–1813), the Russian troops led by General Pavel Tsitsianov tried to take Etchmiadzin, but failed. A few days after the attempt, the Russians returned to Etchmiadzin, where they caught a different Persian force by surprise and routed them. Tsitsianov's forces entered Etchmiadzin, which, according to Auguste Bontems-Lefort, a contemporary French military envoy to Persia, they looted, seriously damaging the Armenian religious buildings. Shortly after, the Russians were forced to withdraw from the area as a result of the successful Persian defense of Erivan. According to Bontems-Lefort, the Russian behaviour at Etchmiadzin contrasted with that of the Persian king, who treated the local Christian population with respect.
On 13 April 1827, during the Russo-Persian War (1826–1828), Etchmiadzin was captured by the Russian General Ivan Paskevich's troops without fight and was formally annexed by Russia, with the Persian-controlled parts of Armenia, roughly corresponding to the territory of the modern Republic of Armenia (also known as Eastern Armenia), according to the 1828 Treaty of Turkmenchay.
The cathedral prospered under Russian rule, despite the suspicions that the Imperial Russian government had about Etchmiadzin becoming a "possible center of the Armenian nationalist sentiment." Due to popular resistance and the personal defiance of Catholicos Mkrtich Khrimian, the edict was canceled in 1905.
During the Armenian genocide, the cathedral of Etchmiadzin and its surrounding became a major center for Turkish Armenian refugees. At the end of 1918, there were about 70,000 refugees in the Etchmiadzin district. A hospital and an orphanage within the cathedral's grounds were established and maintained by the U.S.-based Armenian Near East Relief by 1919. Prior to the May 1918 Battle of Sardarabad, which took place just miles away from the cathedral, the civilian and military leadership of Armenia suggested Catholicos Gevorg (George) V to leave for Byurakan for security purposes, but he refused. The Armenian forces eventually repelled the Turkish offensive and set the foundations of the First Republic of Armenia.
Soviet period
Suppression
After two years of independence, Armenia was Sovietized in December 1920. During the 1921 February Uprising Etchmiadzin was briefly (until April) taken over by the nationalist Armenian Revolutionary Federation, which had dominated the pre-Soviet Armenian government between 1918 and 1920.
In December 1923, the southern apse of the cathedral collapsed. It was restored under Toros Toramanian's supervision in what was the first case of restoration of an architectural monument in Soviet Armenia.
thumb|upright|The Soviet government issued a postage stamp depicting the cathedral in 1978.
During the Great Purge and the radical state atheist policies in the late 1930s, the cathedral was a "besieged institution as the campaign was underway to eradicate religion." The repressions climaxed when Catholicos Khoren I was murdered in April 1938 by the NKVD. In August 1938, Soviet Armenian authorities formally resolved to close Etchmiadzin, convert it into a museum, and never elect a new Catholicos. However, Soviet Armenian leader Grigory Arutinov referred the decision to Stalin for central confirmation, arguing that Etchmiadzin carried international weight and could not be treated as a purely local matter. Within a month, Stalin contacted Arutinov directly and asked whether he still insisted on closing the Catholicosate. Arutinov said he did not insist and the matter was closed. The Soviet leadership valued the Catholicosate primarily as a instrument of influence over the Armenian diaspora.<!--In August 1938 the Armenian Communist Party decided that Echmiadzin monastery was to be closed down, though Moscow appears not to have responded with its approval. --> Isolated from the outside world, the cathedral barely continued to function and its administrators were reduced to some twenty people. The dissident anti-Soviet Armenian diocese in the U.S. wrote that "the great cathedral became a hollow monument."
Revival
Etchmiadzin slowly recovered its religious importance during World War II. The Holy See's official magazine resumed publication in 1944, while the seminary was reopened in September 1945. In 1945 Catholicos Gevorg VI was elected after the seven-year vacancy of the position. The number of baptisms conducted at Etchmiadzin rose greatly: from 200 in 1949 to around 1,700 in 1951. Nevertheless, the cathedral's role was downplayed by the Communist official circles. "For them the ecclesiastical Echmiadzin belongs irrevocably to the past, and even if the monastery and the cathedral are occasionally the scene of impressive ceremonies including the election of a new catholicos, this has little importance from the communist point of view," Walter Kolarz wrote in 1961.
Etchmiadzin revived under Catholicos Vazgen I since the Khrushchev Thaw in the mid-1950s, following Stalin's death. Archaeological excavations were held in 1955–56 and in 1959; the cathedral underwent a major renovation during this period. Catholicos Karekin II declared 2003 the Year of Holy Etchmiadzin.
The most recent restoration of the cathedral began in 2012, focusing on strengthening and restoring the dome and roof. Its ceremonial reopening took place on September 29, 2024, with senior officials in attendance, including Prime Minister Nikol Pashinyan. The main benefactors, including diaspora billionaires Noubar Afeyan and Samvel Karapetyan, who had funded to the renovation, were honored by Catholicos Karekin II.
The initial goal was to address the external structure, primarily repairing roof tiles, but significant issues with the cathedral's physical condition were subsequently uncovered. Critical structural elements, including columns, arches, the dome, and vaults, were found to be severely deteriorated. Restoration efforts employed high-quality materials, such as injection compounds, waterproofing agents, and mortar, most of which were imported from Italy. Additionally, the frescoes and painted surfaces, covering , were meticulously restored. Its 17th century cross, made of thin brass sheets and in a severely deteriorated condition, was replaced with a bronze one that closely replicates its style and size.
Architecture
thumb|The present-day ground plan of Etchmiadzin
Style
Etchmiadzin has a cruciform plan, four free-standing piers, and four projecting apses, which are semicircular on the interior and polygonal on the exterior.
Although the cathedral was renovated many times through the centuries and significant additions were made in the 17th and 19th centuries, it largely retains the form of the building constructed in 483/4,
