Final answer:
While Herodotus reported over 2 million Persian troops at the Battle of Thermopylae, modern scholars estimate around 100,000-150,000, questioning the accuracy of ancient sources. The Greeks confronted them with far fewer troops, notably 10,000 hoplites at the Battle of Marathon. Further investigation could involve archaeological findings and comparing multiple historical records.
Step-by-step explanation:
Estimating the number of Persian troops at the Battle of Thermopylae has been the subject of historical debate. While ancient sources report very high numbers, modern historians typically suggest more conservative figures. Herodotus, the Greek historian, reported that the Persians had a force of over 2 million, however, modern scholars dispute this number and estimate that the Persian force was likely much smaller, typically suggesting figures closer to 100,000-150,000 men.
The Athenians, on the other hand, faced the Persians with a force of around 10,000 hoplites at the Battle of Marathon. As the story goes, the Persians eventually dispatched some of their force to attack Athens directly, which led to a decisive Greek victory where their phalanx formation outmatched the conscripted Persian infantry.
For further investigation into the number of Persian troops, one might consult archaeological evidence, study military logistics of the period (including the limits of supply lines and transportation capabilities), and compare accounts from various historical sources, including those from Persian records if available.