Pheidippides returned back to Athens with the message that the Spartans could not currently offer them any help against their upcoming battle against the Persian forces mustering at Marathon. The Spartan announced that they could not march out of Sparta during the 'ninth day of the first decade', they would have to wait for the next full moon, before they could offer them any assistance.
It has also been questioned by modern historians and military personal as to whether the Athenians whould have waited inside the walls of Athens to wait until the message from Sparta returned or whether the Athenians has already marched out of Athens and camped opposite the Persians at Marathon when the message arrived to them. In short they would have still been inside the city walls of Athens when the message returned. Athens had too much to loose marching out of the city before knowing what the Spartans were going to do. If the Spartans were to march out immediatley, the Persians would have been at a great disadvantage besiging Athens while the Spartans could harase them from the outter perimiter.
In Athens now they needed to think about the next course of action. The Persians had made it clear that they wanted Euboea and Athens burnt to the ground for their part in the Battle of Sardis, Euboea as like most of the islands had fallen into Persian hands, and now with their landing at Marathon, the ball was clearly in the Athenian court, they needed to make the next move.
1-The Persian fleet set sail from Cyprus
2-The islands of Kos and Samos are taken by the Persian fleet
3-The next islands to be taken are Naxos and Paros
4-The island of Delos was taken by the Persians who respect the their holy ground
5-The islands of Tenos and Andros was then taken
6-The city of Karystos in Euboea, surcome and soon after the rest of the island falls into Persian hands. Hippias then advises the Persian Datis to land at Marathon.
Miltiades, who had the most forceful personality among the ten Attic strategoi (Generals), who, in a debate to the Athenian Popular Assembly, put forward that the entire Athenians male hoplite force needed to march out at once and engage the enemy on the Marathon plain. It was a bold decision and contrary to the thinking of many, who preferred to wait for the enemy to advance upon the city itself.
Miltiades however, held the upper hand. He had fought originally for and then against the Persians while he was tyrannt in the Chersonesus. In Athens nobody had greater military experience against Persians than Miltiades. His forceful personality, prior experience and state of fear that Athens was currently under made the Athenians give in to his wishes and march their forces out of Athens as per Miltiades wishes, and march to Marathon.
*01'Histories' by Herodotus; published by Wordsworth 1996 (6.112)
*02'The Greco-Persian Wars' by Peter Green published by University of California Press 1998
*03 Ref to website: http://en.wikipedia.org/wiki/Callias
*04 'Guide to Greece - Vol 1: Central Greece' by Pausanias published by Penguin 1971 Book 1 15.4
Other web sites of interest: