This article brings to light the wide spectrum of cooperation over time and space between the Churches of Syro-Mesopotamia and Egypt, which both reject the decisions of the Council of Chalcedon. Among the ancient Apostolic Churches only these two conserved an unbroken, transparent and full ecclesiastical unity, nurturing the complementary heritages not just at the level of Church hierarchy. They are true sister Churches, also literally: in Semitic languages the word “church” is feminine. The article describes several common elements in liturgy, the circumstances of patriarchs from one Church reigning over the other, ordination of each other’s priests, monasteries built on each other’s territory, where up to hundreds of monks of both denominations served, including famous theologians, writers, translators and scholars. An important place, even today, belongs to the still working monastery of Dayr as-Suryān in Egypt. Its extensive library with unique manuscripts in Syriac was moved, mostly to the Vatican, in the 18 th century. Other important aspects are mutual help with education and church access, as well as Syriac borrowings present in the Coptic liturgy and everyday speech.

This article is written in English.