Obi_Kwiet
It's Stuart, Martha Stuart
Posts: 7,943
Once there are enough elephants, plus paladins, it's hard for them reliably hold the elephants off, and they get murdered if you try to counter attack counter attack. If there are enough, it's going to take time to kill them all, and hand cannoners have such low health that if any thing makes it through to them they're screwed. For elephants the best thing to do is attack food production, rather than trying to take them head on. If you're playing a map like Black Forrest and that's not an option, the only single unit that will do well against them is the Mameluke. Other than that, I personally love massed heavy scorpions with a meat shield like Teutonic knights or halberds.
For lower number (<20) halberds can be pretty effective, but you'll have to make a *bunch*. Persians are definitely one of the best civs in the game. They can be countered, but with great difficulty.
If you can get support from another player, Mongols have a tech. that allows their siege units to move stupidly fast. There's nothing funnier than seeing a horde of forty siege rams rush into an opponent's base.