The War Elephant is best used against mounted units, and is vulnerable to spear/pike men.
The War Elephant is replaced by the following unique units:
Strategy
This powerful early mounted combat unit is a slower, but more powerful counter to units like the Horse Archer.
Civilopedia entry
The war elephant was first used in India and was known to the Persians by the 4th century BC. Using war elephants, Chandragupta Maurya defeated Alexander's successor Seleucus and established the Mauryan Empire. Though Carthage's African war elephants accomplished little subsequently, their presence in Hannibal's army during his transit of the Alps into the heart of Rome in 218 BC established their reputation as a fearsome weapon. The elephant's tactical importance apparently stemmed in large part from its willingness to charge both foot soldiers and cavalry and from the panic that it inspired. Although used in Indian military forces until the 20th century, as with so many traditional weapons, the utility of elephants in war ended with the widespread use of gunpowder.