Tips dealing with pike phalanxes?

[Brennus]

I just wanted to exchange pictures of our empires.

[seleucid empire]

i own all the victory condition provinces plus all of the stepple provinces in the north, sarmatians are wiped out. i also own all of greece macedon eprus and dacia. and i aslo own all of the black sea. i havent gone into south arabia yet
oh and i also own sicily and most of italy

[seleucid empire]

oh also ethipia and axum