Nearly all the crops and many of the weeds come from outside Britain. The cereals - wheat and barley - first arrived from southern and eastern Europe in the neolithic, over 5000 years ago. Some of the existing plants of seashore and hill moved in with these crops to become weeds and have remained in fields to this day. Seeds for many medicinals, dyes, oils and fibres were also mostly imported, as more recently were potato and rapeseed. Other weeds arrived, along with seed and animals from Europe, Asia and North America. As croplands spread, many of the native plants disappeared or retreated to the fringes of managed fields, or found refuge in the margins of woods and wetlands.