Updated October 19, 2018: New entries! Looking back, we hadn't updated our list of the best tower defence games on iOS for a while prior to today.
There's a good reason for this, and it's nothing to do with negligence or laziness. Well, not entirely.
Put simply, the tower defence genre isn't anywhere near as popular as it used to be. We can count the number of notable releases in the genre since September 2016 on one hand.
Still, it remains a fun and mobile-friendly strategy sub genre with some downright classic games. What's more, you still see a little TD magic sprinkled across some of the popular hybrid genres of the moment.
If there's a king of the mobile tower defence games, it has to be the Kingdom Rush series. The original (together with its two follow-ups) sports a near-perfect mix of tight strategic gameplay, intuitive controls, inventive and balanced levels, and beautiful comic book graphics.
The one iOS series that challenges Kingdom Rush for the TD throne is Fieldrunners. The second game in particular takes the classic tower defence template to its natural limits, with an impressive mixture of open and funnelled levels, loads of tower and enemy types, and slick graphics that can still impress four years on.
You might say that Plants vs Zombies is a lane defence game rather than tower defence. We say it still involves defending your base by building, positioning, and upgrading automated defences. And it's still awesome.
Is Clash of Clans really a tower defence game? No more or less than it's a strategy game, or a resource management game. The truth is that CoC pretty much established its own hybrid genre. It's a game of marshalling your resources, arranging your defences, and so much more.
Never has the phrase 'more of the same' been less damning and more welcome than it is with the Kingdom Rush series. This second game doesn't change the core gameplay at all, but it does provide an all new setting and a completely fresh set of towers, heroes, and enemies.
It lacks the scale and sophistication of its sequel, but the original Fieldrunners remains an excellent game in its own right. Subatomic's game established the blueprint for a particular brand of mobile TD that requires you to create snaking death-paths for waves of attackers.
Yes, we're including a third Kingdom Rush game on this list - not because it does anything particularly fresh, but because it's so much better than most of its rivals. Again, there are completely new towers, enemies, and heroes, and that's more than enough.
Royal Revolt is a game in the sub(-sub?)-genre of tower offence. It sets you in a similar asymmetrical battlefield, but switches the perspective so that you are the aggressor. It nails the twist, too, with bold 3D graphics and frantic gameplay.
As one of the more recent additions to this list, Castle Creeps TD is a highly polished example of the tower defence genre. There's not much new here, but like we said in the intro, games like these don't come along as often as they used to.
Chrystal Siege goes with the Kingdom Rush approach to TD, which as you've already seen, is no bad thing. The key twist here is that you can take direct control of your hero and set about laying into baddies directly.
The Anomaly games are another highly esteemed mobile TD franchise, and they come with a similar twist to Royal Revolt - this time you're the attacking swarm running the gauntlet through the enemy's static defences. Anomaly 2 in particular is a total visual treat.
Sentinel 4 arrived blinking into the light some four years after Sentinel 3. As a result, its old school and decidedly hardcore brand of tower defence - packed full of systems and lacking much in the way of hand-holding - is surprisingly refreshing.
Somewhat confusingly, Anomaly Defenders's big twist is to reverse the twist of the earlier Anomaly games. Which essentially means it's a traditional tower defence game - albeit one with some uncommonly accomplished visuals and deeper-than-usual gameplay mechanics.
This console conversion covers an awful lot of ground for a tower defence game, mixing in elements of Angry Birds-like pinging and hack-and-slash action. Perhaps surprisingly, it all sticks together very well indeed.
Castle Doombad's big contribution to the tower defence genre is in flipping the gameplay to a side-on perspective, and then putting you in control of the super villain as hordes of do-gooders storm your trap-laden castle. It's gleeful fun.
Tiny Defense 2, like its predecessor, flips the TD template around to a side-on perspective and makes everything look like a 16-bit mascot platformer. The result is one of the more welcoming TD games of recent times.
It's amazing what a fresh setting can do. This iPad-only tower defence game adopts a 1950s sci-fi B-movie aesthetic and a planetary defence angle, and hey presto! We have a genuinely unique tower defence game.
The Dead Island brand name is here put towards a surprising mixture of TD strategy and hack-and-slash combat. It's not the subtlest slice of strategy on this list, but defending a band of survivors from waves of the undead is sure to put a grim smile on your face.
It might look a bit (okay, a lot) like Minecraft, but Block Fortress hones a surprisingly tight 3D tower defence game out of those familiar building blocks. Pick a place to make your stand, build a fortress, and fend off the enemy waves, jumping in for some crude FPS action where necessary.
The title stands for Over the Top Tower Defence, which is a pretty accurate description. OTTTD lays it on thick with the silly humour and cartoony gore. It also folds in some neat RTS elements to further spice things up.