Large parts of East Frisia were once covered by ombrotrophic (rain-fed) raised bogs which began to develop in the early Atlantic period (early mid-post-glacial). These bogs replaced the preceding forests and also covered prehistoric settlements. They continued to grow vertically and spread laterally until they were reclaimed and cultivated from the Middle Ages onwards. Starting at the margins, peat cutting and reclamation began in the tenth/eleventh centuries AD. In the mid-eighteenth century systematic colonisation of the main bogs began, mostly combined with bog burning. A special East Frisian feature is the so-called Fehn-colonies, i.e. long settlement rows along canals, where peat was cut for fuel for the towns around. In recent times, a new form of bog utilisation was initiated whereby uncut raised bog was brought into agricultural use with the help of artificial fertilizer and some drainage. After peat cutting as a source of fuel for domestic and industrial use ceased in the later twentieth century, the uppermost poorly decomposed peat layers were cut for use in horticulture (plant potting, etc.). In recent years, much effort has been expended in restoring the surviving remnants of raised bog and give them protection within nature reserves.