Suidas s.v. Nemesis
Nemesis : Vengeance, justice, outrage, divine jealousy, fortune. ‘Perceiving Nemesis, the executioner of braggarts, who pursued them with justice.’ And again : ‘he did not escape the notice of Nemesis who opposes all the arrogant, but was compelled to be taught a lesson in his own misfortunes.’ ‘Nemesis was present, she who watches the things of the earth’; or in other words, she who watches unjust acts. Babrios says this in the Fables. And Aelian says : ‘palpable evidence of Nemesis the overseer, chastizing proud and disdainful ways.’ And a proverb : ‘At least Nemesis walks at your feet’; that is to say that the goddess swiftly pursues wrong-doers. ‘Unnoticed she walks at your feet, snaps your haughty neck, and always holds sway over your sustenance with her forearm.’

Pausanias, Description of Greece 1.33.4
A little way inland from Rhamnos is a sanctuary of Nemesis, the most implacable deity to men of violence. It is thought that the wrath of this goddess fell also upon the foreigners [i.e. the Persian army] who landed at Marathon.