In recent times they have been called, chiefly by the Anglicans, the "Assyrian Church", a name which can be defended on archaeological grounds. Brightman, in his "Liturgies Eastern and Western", includes Chaldean and Malabar Catholics and Nestorians under "Persian Rite", and Bishop Arthur Maclean of Moray and Ross (Anglican) who is the best living authority on the existing Nestorians, calls them "East Syrians", which is perhaps the most satisfactory term. The catalogue of liturgies in the British Museum has adopted the usual Catholic nomenclature, calling the rite of the East Syrian Catholics and Nestorians the "Chaldean Rite", that of the South Indian Catholics and schismatics the "Malabar Rite', and that of the West Syrian Monophysites and Catholics the "Syrian Rite", a convenient arrangement in view of the fact that most printed liturgies of these rites are Eastern Rite Catholic.
The language of all three forms of the East Syrian Rite is [[Syriac]], a modern form of which is still spoken by the Nestorians and some of the Catholics. The origin of the rite is unknown. The tradition -resting on the legend of Abgar and of his correspondence with Christ, which has been shown to be apocryphal- is to the effect that [[St. Thomas the Apostle]], on his way to India, established Christianity in Mesopotamia, Assyria, and Persia, and left [[Thaddeus of Edessa|Adaeus]] (or Thaddeus), "one of the Seventy", and [[Maris]] in charge. To these the normal liturgy is attributed, but it is said to have been revised by the Patriarch Yeshuyab III in about 650. Some, however, consider this liturgy to be a development of the Antiochene.
After the [[Council of Ephesus]] (431), the Church of Seleucia-Ctesiphon, which had hitherto been governed by a [[Catholicos|catholicos]] under Antioch, refused to accept the condemnation of Nestorius, cut itself and the Church to the East of it off from the Catholic Church. In 498 the catholicos assumed the title of "Patriarch of the East", and for many centuries this most successful missionary church continued to spread throughout Persia, Tartary, Mongolia, China, India, developing on lines of its own, very little influenced by the rest of Christendom.
At the end of the fourteenth century the conquests of
[[Tamerlane ]] all but destroyed this flourishing Church at one blow, reduced it to a few small communities in Persia, Turkey in Asia, Cyprus, South India, and the Island of [[Socotra]]. The Cypriote Nestorians united themselves to Rome in 1445; in the sixteenth century there was a schism in the patriarchate between the rival lines of [[Mar Shimun]] and [[Mar Elia]]; the Christianity of Socotra, such as it was, died out about the seventeenth century; the Malabarese Church divided into Catholics and Schismatics in 1599, the latter deserting Nestorianism for Monophysitism and adopting the [[West Syrian Rite]] about fifty years later; in 1681 the Chaldean Unia, which had been struggling into existence since 1552, was finally established, and in 1778 received a great accession of strength in the adhesion of the whole Mar Elia patriarchate, and all that was left of the original Nestorian Church consisted of the inhabitants of a district between the Lakes of Van and Urmi and Tigris, and outlying colony in Palestine. These have been further reduced by a great massacre by the Kurds in 1843, and the secession of a large number to the Russian Church within the last few years.
In the late nineteenth century there was an attempt to form an "Independent Catholic Chaldean Church", on the model of the "Old Catholics". This resulted in separating a few from the Eastern Rite Catholics.