I want to know the answer to the following question:
Who invaded the Archaemenid Empire in 334BC?
All the background I'm provided with is that "In the middle of the 2nd century BC, the Parthian Empire rose to become the main power in Iran, and the century-long geopolitical arch-rivalry between Romans and Parthians began, culminating in the Roman–Parthian Wars.". Is that enough to answer the question?