Themistocles believed that the chief thing necessary for Athens was a fleet, and he persuaded the Athenians, though with great difficulty for they could not at first see the necessity, to build ships. There was not very much money in Athens just then, and without money ships could not be built. But at this critical time, an unexpectedly large sum of money was paid into the public treasury. This was {156} the revenue from the silver mines at Laurium in the south of Attica, which the Athenians were intending to divide amongst themselves. "Then Themistocles persuaded them to give up this plan of division and to make for themselves with this money two hundred ships." This they did, and they also improved the harbour of Athens, and henceforward, little by little, turning and drawing the city down towards the sea in the belief that with their ships they might be able to repel the Persians and command Greece, Themistocles, so Plato tells us, turned the Athenians from steady soldiers into mariners and seamen and gave occasion for the reproach against him, that he took away from them the spear and the shield and bound them to the bench and the oar.[6] Themistocles did not accomplish this without opposition. He had a rival in Athens, Aristeides, a man who had grown up with him and played with him as a boy, but who had always taken the opposite sides in whatever they were doing. Unlike Themistocles, Aristeides belonged to a noble family, and whenever Themistocles took the side of the people, Aristeides favoured the nobles. Even as boys they were at variance with each other, and they soon made proof of their natural inclinations; the one being ready, adventurous and subtle, engaging readily and eagerly in everything; the other of a staid and settled temper, intent on the exercise of justice, not admitting any degree of falsity or trickery, no not so much as at his play.[7] {157} Of all his virtues, it was the _justice_ of Aristeides which most appealed to the people; it never failed under any circumstances, and so they gave him the surname of the _Just_. Now Aristeides believed that the building of a navy for Athens was too great a change from the former policy of the city. The Athenians had won the battle of Marathon and had thereby secured their reputation as soldiers, and he thought it very ill-advised and dangerous to depart from the old traditions and to put all their strength into war ships. Themistocles thought otherwise, and the two leaders came into violent conflict with each other.