What are Gems and how can I get them?

Ooh, Shiny Gems! Gems are the premium currency in the game and can be used to hire Mercenaries, exchange for Gold, buy special offer packs, by purchasing with an in-app purchase, and in the daily login bonus on Day 5.

You can purchase Gems from the Black Market by tapping on either the open treasure chest icon in the bottom left-hand corner of the screen or by tapping the + icon on the Gem icon on the left hand of the screen.

You can also build a gem mine to get some additional gems every day.