It was used as a method to cure many aliments, such as fevers, aches and pains, but it was also used as a form of contraception, similar to the modern use of 'the Pill'.
Its seeds were shaped like elongated hearts, and it is possible this is the origin of the heart symbol we use today.
A coin from Cyrene depicting a Silphium flower and stalk. (Source:1889 edition of Principal Coins of the Ancients. Wikipedia)