According to historical dates the following events are arranged in descending order (from the recent period). Settlements in Arikamedu (between 2200 and 1900 years ago). Beginning of the composition of Sangam literature (about 2300 years ago). Increase in the use of iron, cities, punch marked coins (about 2500 years ago). Beginning of the use of iron in the subcontinent (about 3000 years ago).