Terp (plural terpen) is a Frisian term for a hillock, mound or knoll used for refuge from floods. Historical Frisian settlements were built on artificial terpen measuring up to 15 m in height to be safe from the floods in periods of rising sea levels. The first terp-building period dates from 500 BC, the second from 200 BC to 50 BC. In the mid 3rd century, the rise of sea level was so dramatic that the clay district was deserted, and settlers returned only around AD 400. A third terp-building period dates from AD 700 (Old Frisian times). This article needs to be cleaned up to conform to a higher standard of quality. ... Centuries: 7th century BC - 6th century BC - 5th century BC Decades: 550s BC - 540s BC - 530s BC - 520s BC - 510s BC - 500s BC - 490s BC - 480s BC - 470s BC - 460s BC - 450s BC Events and Trends 509 BC - Foundation of the Roman Republic 508 BC - Office of pontifex maximus created... Centuries: 3rd century BC - 2nd century BC - 1st century BC Decades: 250s BC 240s BC 230s BC 220s BC 210s BC - 200s BC - 190s BC 180s BC 170s BC 160s BC 150s BC Years: 205 BC 204 BC 203 BC 202 BC 201 BC - 200 BC - 199 BC 198 BC... // Events Saint Adamnan convinces 51 kings to adopt Cáin Adomnáin defining the relationship between women and priests. ... Old Frisian was the West Germanic language spoken between the 8th and 16th centuries by the people who, from their ancient homes in North Germany and Denmark, had settled in the area between the Rhine and Elbe on the European North Sea coast in the 4th and 5th centuries. ...