The art created in Armenia's historical province of Artsakh, the largest part of which is known today as Nagorno Karabakh, constitutes one of the important chapters in the history of Armenian art. It has progressed through the same major stages as did Armenian art in a larger sense: from pre-Christian times to the adoption of Christianity early in the fourth century, through the Middle Ages, and from there — to the era of modernity. As in many other Christian cultures, the principal expression of Artsakh's art in the Middle Ages was through ecclesiastical architecture: churches, cathedrals, chapels and monasteries. Most other forms of art in that period, including illuminated manuscripts, khachkars (unique-to-Armenia stone slabs with engraved crosses) and mural paintings were likewise tied to Artsakh's religious life and its primary institution — the Armenian Apostolic Church