how do coins help us in the reconstruction of historical events

Any intact coin from the past helps us know 

a) rulers at the time, structures or landmarks that were built before the date on the coin 

b) a sample of their writing or number system 

c) the extent of their ability to make coinage, the types of metals they could smelt, the quality and purity of that metal, the processes they struck or poured the coins, which can tell a lot about the culture's technological achievement. 

d) a concrete date that the civilization was in power

Of late historians attach much importance to coins as a source material for the reconstruction of ancient Indian history. For no other source reveals such information as revealed by the coins.

For instance, the metal or metals used in the coins help to understand the advancement made in the production of these.

Distribution of coins indicate the areas that" had been under the control of the particular king who issued such coins. Again, coins also throw light on the economic history.

Also the coins in which names of kings appear enable historians to know about the chronology of a ruling dynasty.

The coins issued particularly by the Kushanas refer to the dates on which they were put into circulation. This helps a lot to reconstruct an accurate history of the period.