There were various other states and cities in Greece, but Athens and Sparta were at this time the most considerable, and they were altogether the most resolute and determined in their refusal to submit to the Persian sway. In fact, so well known and understood was the spirit of defiance with which these two powers were disposed to regard the Persian invasion, that when Xerxes sent his summons demanding submission, to the other states of Greece, he did not send any to these. When Darius invaded Greece some years before, he had summoned Athens and Sparta as well as the others, but his demands were indignantly rejected. It seems that the custom was for a government or a prince, when acknowledging the dominion of a superior power, to send, as a token of territorial submission, a little earth and water, which was a sort of legal form of giving up possession of their country to the sovereign who claimed it. Accordingly, when Darius sent his embassadors into Greece to summon the country to surrender, the embassadors, according to the usual form, called upon the governments of the several states to send earth and water to the king. The Athenians, as has been already said, indignantly refused to comply with this demand. The Spartans, not content with a simple refusal, seized the embassadors and threw them into a well, telling them, as they went down, that if they wanted earth and water for the King of Persia, they might get it there. The Greeks had obtained some information of Xerxes's designs against them before they received his summons. The first intelligence was communicated to the Spartans by Demaratus himself, while he was at Susa, in the following singular manner. It was the custom, in those days, to write with a steel point on a smooth surface of wax. The wax was spread for this purpose on a board or tablet of metal, in a very thin stratum, forming a ground upon which the letters traced with the point were easily legible. Demaratus took two writing-tablets such as these, and removing the wax from them, he wrote a brief account of the proposed Persian invasion, by tracing the characters upon the surface of the wood or metal itself, beneath; then, restoring the wax so as to conceal the letters, he sent the two tablets, seemingly blank, to Leonidas, king of Sparta. The messengers who bore them had other pretexts for their journey, and they had various other articles to carry. The Persian guards who stopped and examined the messengers from time to time along the route, thought nothing of the blank tablets, and so they reached Leonidas in safety.