Armies got upgraded with C3C - extra movement and a lot of attacks depending on speed.
They are not invincible, you might lose one army of four to a single defender, but according to the holy law of preserve random seed 4 single attackers would have lost the same way.
But if you win - you probably saved 2-3 units, and armies can crack even mountain fortresses and kill one defending unit, a thing no other unit could do.
A victorious army also enables a slew of new small wonders that are rather good.
They are not invincible, you might lose one army of four to a single defender, but according to the holy law of preserve random seed 4 single attackers would have lost the same way.
But if you win - you probably saved 2-3 units, and armies can crack even mountain fortresses and kill one defending unit, a thing no other unit could do.
A victorious army also enables a slew of new small wonders that are rather good.