Old Believers' prayer houses are an indispensable part of Latvia's cultural environment, especially in the eastern part of the country. Although the Old Believers community has participated in the shaping of the region's specific cultural and social environment for more than three hundred years, its sacred architecture in Eastern Latvia has been little examined so far and attention has mainly been paid to the sacred items found in their prayer houses - icons and books. In the world-wide cultural context, Old Believers are known as preservers of the unique ancient culture of the Russian Orthodox Church. Their origins date back to the mid-17th century reforms introduced by Patriarch Nikon which resulted in the schism between the ruling Russian Orthodox Church and dissident Old Believers. Opponents of these revisions endured wide-scale punitive actions and persecutions. The first organized groups of Old Believers appeared in eastern Latvia soon after the church reform began; they had come mostly from Novgorod, Pskov and other territories west of Moscow. From eastern Latvia Old Believers gradually reached other parts of Latvia, Lithuania and Estonia. Eleven towns in Latvia became noted centres of Old Believer culture and religion, featuring the most significant communities of Old Believers in eastern Latvia. Each of these towns has one prayer house, except Daugavpils which has six Old Believers' prayer houses. The prayer house has always been and still is the centre of every community of Old Believers. It performs not just sacred but also secular functions. The premises are used for active educational work and gatherings and conferences of the Old Believers community. The Old Believers of eastern Latvia belong to the so-called Bezpopovtsy ('priestless') branch without clergy and liturgy in their services. The lack of an altar emerges as the most distinctive element of Old Believers sacred architecture.