chiton a Greek garment; a sleeveless piece of linen or wool secured at the shoulders by brooches and at the waist by a belt

Circe a Greek goddess of magic

Clytius a giant created by Gaea to absorb and defeat all of Hecate’s magic

Cocytus the River of Lamentation in Tartarus, made of pure misery

cohort one of ten divisions in a Roman legion; a group of soldiers

Colosseum an elliptical amphitheater in the center of Rome, Italy. Capable of seating fifty thousand spectators, the Colosseum was used for gladiatorial contests and public spectacles, such as mock sea battles, animal hunts, executions, reenactments of famous battles, and dramas.

cornucopia a large horn-shaped container overflowing with edibles or wealth in some form. The cornucopia was created when Heracles (Roman: Hercules) wrestled with the river god Achelous and wrenched off one of his horns.

Cupid Roman god of love. Greek form: Eros

Cyclops a member of a primordial race of giants (Cyclopes, pl.), each with a single eye in the middle of his or her forehead

Daedalus in Greek mythology, a skilled craftsman who created the Labyrinth on Crete in which the Minotaur (part man, part bull) was kept

Damasen giant son of Tartarus and Gaea; created to oppose Ares; condemned to Tartarus for slaying a drakon that was ravaging the land

Demeter the Greek goddess of agriculture; a daughter of the Titans Rhea and Kronos. Roman form: Ceres

denarius (denarii, pl.) the most common coin in the Roman currency system

Diocletian the last great pagan emperor, and the first to retire peacefully; a demigod (son of Jupiter). According to legend, his scepter could raise a ghost army.

Diomedes a principal Greek hero in the Trojan War

Dionysus the Greek god of wine and revelry; a son of Zeus. Roman form: Bacchus

Doors of Death the doorway to the House of Hades, located in Tartarus. The Doors have two sides—one in the mortal world and one in the Underworld.

drachma the silver coin of Ancient Greece

drakon a gigantic yellow and green serpent-like monster, with frills around its neck, reptilian eyes, and huge talons; it spits poison

dryads tree nymphs

Earthborn Gegenees in Greek; monsters that wear only a loincloth and have six arms

eidolons possessing spirits

Elysium the section of the Underworld where those who are blessed by the gods are sent to rest in eternal peace after death

empousa a vampire with fangs, claws, a bronze left leg, a donkey right leg, hair made of fire, and skin as white as bone. Empousai [pl.] have the ability to manipulate the Mist, change shape, and charmspeak in order to attract their mortal victims.

Epirus a region presently in northwestern Greece and southern Albania

Eris goddess of strife

Eros Greek god of love. Roman form: Cupid

faun a Roman forest god, part goat and part man. Greek form: satyr

Favonius Roman god of the West Wind. Greek form: Zephyros

Fields of Asphodel the section of the Underworld where people who lived neither a good nor a bad life are sent after death

Fields of Punishment the section of the Underworld where people who were evil during their lives are sent after death to face eternal punishment for their crimes

Furies Roman goddesses of vengeance; usually characterized as three sisters—Alecto, Tisiphone, and Megaera; the children of Gaia and Uranus. They reside in the Underworld, tormenting evildoers and sinners. Greek form: the Erinyes

Gaea the Greek earth goddess; mother of Titans, giants, Cyclopes, and other monsters. Roman form: Terra

Geras god of old age

Geryon a monster with three bodies that was slain by Heracles/Hercules

gladius a short sword

Graecus the word Romans used for Greek

greaves shin armor

Greek fire an incendiary weapon used in naval battles because it can continue burning in water

gris-gris In this New Orleans Voodoo practice named after the French word for gray (gris), special herbs and other ingredients are combined and put into a small red flannel bag that is worn or stored to restore the balance between the black and white aspects of a person’s life.

gryphon a creature with the forequarters (including talons) and wings of an eagle and the hindquarters of a lion

Hades the Greek god of death and riches. Roman form: Pluto

Hannibal a Carthaginian commander who lived between 247 and 183/182 BCE and is generally considered to be one of the greatest military strategists in history. One of his most famous achievements was marching an army, which included war elephants, from Iberia over the Pyrenees and the Alps into northern Italy.

harpy a winged female creature that snatches things

Hecate goddess of magic and crossroads; controls the Mist; daughter of Titans Perses and Asteria

Hemera goddess of day; daughter of Night

Hephaestus the Greek god of fire and crafts and of blacksmiths; the son of Zeus and Hera, and married to Aphrodite. Roman form: Vulcan

Hera the Greek goddess of marriage; Zeus’s wife and sister. Roman form: Juno

Heracles the son of Zeus and Alcmene; the strongest of all mortals. Roman form: Hercules

Hercules the son of Jupiter and Alcmene, who was born with great strength. Greek form: Heracles

Hermes Greek god of travelers; guide to spirits of the dead; god of communication. Roman form: Mercury

Hesiod a Greek poet who speculated that it would take nine days to fall to the bottom of Tartarus

Horatius a Roman general who single-handedly held off a horde of invaders, sacrificing himself on a bridge to keep the barbarians from crossing the Tiber River. By giving his fellow Romans time to finish their defenses, he saved the Republic.

House of Hades a place in the Underworld where Hades, the Greek god of death, and his wife, Persephone, rule over the souls of the departed; an old temple in Epirus in Greece

Hyperion one of the twelve Titans; Titan lord of the east

Hypnos Greek god of sleep. Roman form: Somnus

hypogeum the area under a coliseum that housed set pieces and machinery used for special effects

Iapetus one of the twelve Titans; lord of the west; his name means the Piercer. When Percy fought him in Hades’s realm, Iapetus fell into the River Lethe and lost his memory; Percy renamed him Bob.

ichor the golden fluid that is the blood of gods and immortals

Imperial gold a rare metal deadly to monsters, consecrated at the Pantheon; its existence was a closely guarded secret of the emperors

Janus Roman god of doorways, beginnings, and transitions; depicted as having two faces, because he looks to the future and to the past

Juno the Roman goddess of women, marriage, and fertility; sister and wife of Jupiter; mother of Mars. Greek form: Hera

Jupiter the Roman king of the gods; also called Jupiter Optimus Maximus (the best and the greatest). Greek form: Zeus

Kampê a monster with the upper body of a snake-haired woman and the lower body of a drakon; appointed by the Titan Kronos to guard the Cyclopes of Tartarus. Zeus slew her and freed the giants from their prison to aid him in his war against the Titans.

katobleps a cow monster whose name means “down-looker” (katoblepones, pl.). They were accidentally imported to Venice from Africa. They eat poisonous roots that grow by the canals and have a poisonous gaze and poisonous breath.

Katoptris Piper’s dagger

Kerkopes a pair of chimpanzee-like dwarfs who steal shiny things and create chaos

Khione the Greek goddess of snow; daughter of Boreas

Koios one of the twelve Titans; Titan lord of the north

Krios one of the twelve Titans; Titan lord of the south

Kronos the youngest of the twelve Titans; the son of Ouranos and Gaea; the father of Zeus. He killed his father at his mother’s bidding. Titan lord of fate, harvest, justice, and time. Roman form: Saturn

Labyrinth an underground maze originally built on the island of Crete by the craftsman Daedalus to hold the Minotaur (part man, part bull)

Laistrygonian giant a monstrous cannibal from the far north

Lar a house god, ancestral spirit (Lares, pl.)

legionnaire Roman soldier

lemures Roman term for angry ghosts

Leto daughter of the Titan Koios; mother of Artemis and Apollo with Zeus; goddess of motherhood

Lotus Hotel a casino in Las Vegas where Percy, Annabeth, and Grover lost valuable time during their quest after eating enchanted lotus blossoms

Mansion of Night Nyx’s palace

manticore a creature with a human head, a lion’s body, and a scorpion’s tail

Mars the Roman god of war; also called Mars Ultor. Patron of the empire; divine father of Romulus and Remus. Greek form: Ares

Medea a follower of Hecate and one of the great sorceresses of the ancient world

Mercury Roman messenger of the gods; god of trade, profit, and commerce. Greek form: Hermes

Minerva the Roman goddess of wisdom. Greek form: Athena

Minos king of Crete; son of Zeus; every year he made King Aegus pick seven boys and seven girls to be sent to the Labyrinth, where they would be eaten by the Minotaur. After his death he became a judge in the Underworld.

Minotaur a monster with the head of a bull on the body of a man

Mist a magic force that disguises things from mortals

Mount Tamalpais the site in the Bay Area (Northern California) where the Titans built a palace

naiads water nymphs

Necromanteion the Oracle of Death, or House of Hades in Greek; a multileveled temple where people went to consult with the dead

Neptune the Roman god of the sea. Greek form: Poseidon

New Rome a community near Camp Jupiter where demigods can live together in peace, without interference from mortals or monsters

Notus Greek god of the South Wind. Roman form: Auster

numina montanum Roman mountain god (montana, pl). Greek form: ourae

nymph a female nature deity who animates nature

nymphaeum a shrine to nymphs

Nyx goddess of night; one of the ancient, firstborn elemental gods

Odysseus legendary Greek king of Ithaca and the hero of Homer’s epic poem The Odyssey. Roman form: Ulysses

Ogygia the island home—and prison—of the nymph Calypso

ourae Greek for mountain god. Roman form: numina montanum

Ouranos father of the Titans

Pasiphaë the wife of Minos, cursed to fall in love with his prize bull and give birth to the Minotaur (part man, part bull); mistress of magical herbal arts

Pegasus in Greek mythology, a winged divine horse; sired by Poseidon, in his role as horse-god, and foaled by the Gorgon Medusa; the brother of Chrysaor

Periclymenus an Argonaut, the son of two demigods, and the grandson of Poseidon, who granted him the ability to change into various animals

peristyle entrance to an emperor’s private residence

Persephone the Greek queen of the Underworld; wife of Hades; daughter of Zeus and Demeter. Roman form: Proserpine

phalanx a compact body of heavily armed troops

Phlegethon the River of Fire that flows from Hades’s realm down into Tartarus; it keeps the wicked alive so they can endure the torments of the Fields of Punishment

pilum (pila, pl.) a javelin used by the Roman army

Pluto the Roman god of death and riches. Greek form: Hades

Polybotes the giant son of Gaea, the Earth Mother

Polyphemus the gigantic one-eyed son of Poseidon and Thoosa; one of the Cyclopes

Porphyrion the king of the giants in Greek and Roman mythology

Poseidon the Greek god of the sea; son of the Titans Kronos and Rhea, and brother of Zeus and Hades. Roman form: Neptune

praetor an elected Roman magistrate and commander of the army