Hi Deepak,

The administration of revenue involved collection of taxes from various sources-mines, forests (vana) plantations (setu), pastures (vraja), etc. According to the Arthashastra, the cities collected 21 kinds of taxes.

Tolls, lines, fees, assaying department for measures and weights, police, passports, currency, manufacturers of yarn, oil, ghee and sugar, slaughter­houses, liquor-vends, goldsmiths, warehouses, gam­bling dens, buildings, prostitutes, guilds of carpenters and artisans, and temples were the main sources of revenue for the Mauryan Empire.

Feel free to ask doubts in the Comment Section.

I hope this information helps you.

Good Luck!

Hello,

Citadel is kind of modern city which has high raised buildings which is same like captial of a state and deals with most economic value and lower town has residential buildings and home business like shops are done at that place.  The ground level of citadel is higher than citadel and lower town is located at the low side of the town for which it is called lower town.

Lower town was a large settlement area during the harappa era.

For more details search on the web you will get all the details.

Hope it help!