The is an Iron Age era in the history of Japan traditionally dated 300 BC to AD 300. It is named after the neighborhood of Tokyo where archaeologists first uncovered artifacts and features from that era. Distinguishing characteristics of the Yayoi period include the appearance of new pottery styles and the start of an intensive rice agriculture in paddy fields. A hierarchical social class structure dates from this period. Techniques in metallurgy based on the use of bronze and iron were also introduced to Japan in this period.