Gylippus: Spartan general sailing to Syracuse in 414; provided turning point in Syracusan campaign--broke Athenian siege, defeated Nicias and Demosthenes. Led to Spartan victory at Syracuse and the capturing of the Athenian captains/generals, including Nicias, whom were subsequently put to death.
Gongylus: commander of Corinthian fleet from Leucas to encourage the Syracusans to hold through the siege for just a bit longer; herald the coming of Gylippus
Nicias: Athenian politican/ general. Part of the aristocracy. Became principle rival of Clean after the death of Pericles. Desired to obtain peace with Sparta on favorable terms to Athens ASAP. Helped settle the Peace of Nicias in 421 BC, which was ultimately discarded, and he was appointed general of invasion in Sicily. Successful in taking Syracuse until Gylippus showed up and routed them. Noted by Thucydides as a pretty decent guy who did not deserve his fate.
Demosthenes: general sent to help Nicias when Nicias asked to resign, a request refused by the Athenian council. Initially successful, backlash of the night operation where many of his own soldiers died. After defeat by Gylippus, wanted to return home but due to a lunar eclipse and Nicias's superstitious nature, they were to remain in Syracuse waters for 27 more days in which both generals were captured and executed.
Agis: Actually Agis II, King of Sparta between 427-401 BC. Led army of Peloponnesians to invade Attica in 413; destroyed part of the country land and at approx 13 miles from Athens built a fortification, probably to instill fright in the Athenians. Had to return home due to a series of earthquakes
Spartiate: a full citizen of Sparta, member of the highest military caste
Plemmyrium: site of Athenian fortification where the Athenians hold a battle against the Poleponnesians; win due to the Syracusans' major inexperience with naval conflict. Managed to capture the forts which contained many warehouses of food, grain, ships, etc.
Peltasts: lightly armed troops who could move much more quickly than the heavily and expensively armed hoplites
Eurymedon: the other Athenian commander sent to help Nicias along with Demosthenes; stopped at Corcyra along the way to help the democratic party overtake the oligarchs and watched as the democrats slaughtered them. Was originally sent to Sicily to negotiate a peace with the Syracusan general Hermocrates, which they did. Anthens, however, did not find it agreeable and subjected Eurymedon to a heavy fine. Killed during one of the battles at Syracuse.
Paean: the war chant sung by troops going into battle; led to the nighttime confusion during one of the battles with Syracuse that Demosthenes ordered; many were killed as a result.
Hermocrates: general of Syracuse, chief advisor to Gylippus during the siege of Syracuse; sent a deceptive message to the fleeing Athenians stating that they should hold off on leaving because the roads were heavily guarded. The Athenians complied, and that gave time for the Peloponnesians to guard the roads and ambush them, slaughtering most of the army.