Given the intermixing of peoples and settlements in the region over the centuries, it is not always easy to separate Amazigh and non-Amazigh architectural features; however, there are architectural types and features associated with predominantly Amazigh areas of Morocco (particularly the rural Atlas mountains and Saharan regions) which are sufficiently distinctive to constitute their own characteristic styles. Because the relevant structures are made of rammed earth or mud-brick, which requires regular maintenance for preservation, the existing examples can rarely be dated reliably past the 19th or even 20th centuries. Nonetheless, some characteristics of Berber architecture in North Africa – such as the regional forms of mosques – have been established for roughly a millennium.