Sword is the most combat-strong weapon you can give your minions. Sword has no use other than for combat against enemy minions and ogres.
Sword can be unlocked with exp, and costs 1 - 5 gold, depending on the number of minions in your tribe. Once unlocked, it moves to the left side of the screen, from where you can drag it onto any minion without a tool or weapon.
Sword is used exclusively for fights. When a minion with a sword gets in range of an enemy, they will move to a single enemy minion and start attacking, like other melee weapons.
In any situation, the minions with sword are the first ones attacked. Unless a fight is very unbalanced, this mean that your knight will sustain damage during a fight.
Sword acts much like other melee tools and weapons, except for one thing: the attack rate. Sword has a quicker attack rate than other weapons, making it very useful for combat. Minions with sword hit first and usually kill first, unless the enemy minion has much better gear and/or is lucky with their shield blocking.
Tips and Tricks Edit
It's not a bad idea to have a tribe of nothing but sword minions in the end-game. You can farm resources off of fights, and if you have legion helmets and steel shields it will be very difficult for opponents to beat you. This requires a lot of gold, though, so if you're going this route you will probably want to kill off some archers or lumberjacks in order to get miners.
If you are low on resources, however, stocking up on knights is probably not the best idea. If you lose minions in fights and you don't have lumberjacks or miners, you won't be able to replace minions and it will be much easier for opponents to chase you down and destroy your tribe.