Updated: April 21, 2021: Wording changed, corrected some bits

Remember when you couldn't swing a cat on the Google Play Store without it being shot to pieces by an automated turret?

Those were the days when the tower defence games genre on Android reigned supreme. If you're new to these parts, and to the tower defence genre in general, then a little explanation might be in order.

Tower defence - or TD as it is often abbreviated - takes some of real time strategy's frenetic live war-mongering, a little of turn based strategy's thoughtful unit placement, and condenses it into a format that's fit for mobile play.

There are various strains of TD, but in general they involve laying down automated defensive turrets ahead of incoming waves of enemy attacks. Get the placement and the mix of units right, and you'll form an impenetrable screen of death.

While we don't get as many tower defence games for Android as we used to, modern examples have started splicing in elements of other genres. Which means there's plenty of life in the old TD dog yet.