The Chấn line (Vietnamese: chi Chấn; chữ Hán: 支震; chi can also be translated to as branch) was the fourth dynasty of Hùng kings of the Hồng Bàng period of Văn Lang (now Vietnam).

Starting 2252 B.C., the line refers to the rule of Bửu Lang and his successors, when the seat of government was centered at Phú Thọ.

[3] The evidence for early Vietnamese calendar system was recorded on stone tools dating back 2200–2000 BC.

Parallel lines were carved on the stone tools as a counting instrument involving the lunar calendar.

[5] Also during this time, population from the mountainous areas moved out and began to settle in the open along the rivers to join the agricultural activities.