Achilles    the best fighter of the Greeks who besieged Troy in the Trojan War; extraordinarily strong, courageous, and loyal, he had only one weak spot: his heel

Admetus    the king of Pherae in Thessaly; Zeus punished Apollo by sending him to work for Admetus as a shepherd

Aeolus    the Greek god of the winds

Agamemnon    king of Mycenae; the leader of the Greeks in the Trojan War; courageous, but also arrogant and overly proud

agora    Greek for gathering place; a central outdoor spot for athletic, artistic, spiritual, and political life in ancient Greek city-states

Ajax    Greek hero with great strength and courage; fought in the Trojan War; used a large shield in battle

ambrosia    food of the gods; has healing powers

amphitheater    an oval or circular open-air space used for performances or sporting events, with spectator seating built in a semicircle around the stage

Aphrodite    the Greek goddess of love and beauty

apodesmos    a band of material that women in ancient Greece wore around the chest, particularly while participating in sports

Apollo    the Greek god of the sun, prophecy, music, and healing; the son of Zeus and Leto, and the twin of Artemis

Ares    the Greek god of war; the son of Zeus and Hera, and half brother to Athena

Argo    the ship used by a band of heroes who accompanied Jason on his quest to find the Golden Fleece

Argonauts    a band of heroes who sailed with Jason on the Argo, in search of the Golden Fleece

Artemis    the Greek goddess of the hunt and the moon; the daughter of Zeus and Leto, and the twin of Apollo

Asclepius    the god of medicine; son of Apollo; his temple was the healing center of ancient Greece

Athena    the Greek goddess of wisdom

Athena Parthenos    a giant statue of Athena; the most famous Greek statue of all time

ballista (ballistae, pl.)    a Roman missile siege weapon that launched a large projectile at a distant target

Batavi    an ancient tribe that lived in modern-day Germany; also an infantry unit in the Roman army with Germanic origins

Briseis    a princess captured by Achilles during the Trojan War, causing a feud between Achilles and Agamemnon that resulted in Achilles refusing to fight alongside the Greeks

Bunker Nine    a hidden workshop Leo Valdez discovered at Camp Half-Blood, filled with tools and weapons; it is at least two hundred years old and was used during the Demigod Civil War

Caesar Augustus    the founder and first emperor of the Roman Empire; adopted son and heir of Julius Caesar (see also Octavian)

Calliope    the muse of epic poetry; mother of several sons, including Orpheus

Calypso    the goddess nymph of the mythical island of Ogygia; a daughter of the Titan Atlas; she detained the hero Odysseus for many years

Camp Half-Blood    the training ground for Greek demigods, located in Long Island, New York

Camp Jupiter    the training ground for Roman demigods, located between the Oakland Hills and the Berkeley Hills, in California

Cassandra    the daughter of King Priam and Queen Hecuba; had the gift of prophecy, but was cursed by Apollo so that her predictions were never believed, including her warning about the Trojan Horse

catapult    a military machine used to hurl objects

Cave of Trophonius    a deep chasm home to the Oracle Trophonius; its extremely narrow entrance required a visitor to lie flat on his back before being sucked into the cave; called “The Cave of Nightmares” due to the terrifying accounts of its visitors

Celestial bronze    a rare metal deadly to monsters

centaur    a race of creatures that is half-human, half-horse

Ceres    the Roman god of agriculture; Greek form: Demeter

Chiron    a centaur; the camp activities director at Camp Half-Blood

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

Chrysothemis    a daughter of Demeter who won Apollo’s love during a music contest

Circe    a Greek goddess of magic

Cloacina    goddess of the Roman sewer system

Clytemnestra    the daughter of the king and queen of Sparta; married and later murdered Agamemnon

Colosseum    an elliptical amphitheater in the center of Rome, Italy, capable of seating fifty thousand spectators; used for gladiatorial contests and public spectacles such as mock sea battles, animal hunts, executions, re-enactments of famous battles, and dramas

Colossus Neronis (Colossus of Nero)    a gigantic bronze statue of Emperor Nero; was later transformed into the sun god with the addition of a sunray crown

Cretan    of the island of Crete

Crommyon    a village in ancient Greece where a giant wild sow wreaked havoc before it was killed by Theseus

cuirass    leather or metal armor consisting of a breastplate and backplate worn by Greek and Roman soldiers; often highly ornamented and designed to mimic muscles

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

Cyrene    a fierce huntress with whom Apollo fell in love after he saw her wrestle a lion; Apollo later transformed her into a nymph in order to extend her life

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

Daphne    a beautiful naiad who attracted Apollo’s attention; she was transformed into a laurel tree in order to escape him

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

dimachaerus    a Roman gladiator trained to fight with two swords at once

Dionysus    the Greek god of wine and revelry; the son of Zeus; activities director at Camp Half-Blood

Domus Aurea    Emperor Nero’s extravagant villa in the heart of ancient Rome, built after the Great Fire of Rome

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

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

dryads    tree nymphs

Erebos    a place of darkness between earth and Hades

Eros    the Greek god of love

Erythaea    an island where the Cumaean Sibyl, a love interest of Apollo, originally lived before he convinced her to leave it by promising her a long life

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

Gaea    the Greek earth goddess; mother of Titans, giants, Cyclopes, and other monsters

Germani (Germanus, sing.)    tribal people who settled to the west of the Rhine river

Golden Fleece    this hide from a gold-haired winged ram was a symbol of authority and kingship; it was guarded by a dragon and fire-breathing bulls; Jason was tasked with obtaining it, resulting in an epic quest

Gorgons    three monstrous sisters (Stheno, Euryale, and Medusa) who have hair of living, venomous snakes; Medusa’s eyes can turn the beholder to stone

Great Fire of Rome    a devastating fire that took place in 64 CE, lasting for six days; rumors indicated that Nero started the fire to clear space for the building of his villa, Domus Aurea, but he blamed the Christian community for the disaster

greaves    shin armor

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

Grove of Dodona    the site of the oldest Greek Oracle, second only to the Delphi; the rustling of trees in the grove provided answers to priests and priestesses who journeyed to the site

Hades    the Greek god of death and riches; ruler of the Underworld

harpy    a winged female creature that snatches things

Hebe    the Greek goddess of youth; daughter of Zeus and Hera

Hecate    goddess of magic and crossroads

Hephaestus    the Greek god of fire and crafts and of blacksmiths; the son of Zeus and Hera, and married to Aphrodite

Hera    the Greek goddess of marriage; Zeus’s wife and sister

Hermes    Greek god of travelers; guide to spirits of the dead; god of communication

Herodotus    a Greek historian known as the “Father of History”

Hestia    Greek goddess of the hearth

hippocampi (hippocampus, sing.)    half-horse, half-fish creatures

hippodrome    an oval stadium for horse and chariot races in ancient Greece

Hittites    a group of people who lived in modern Turkey and Syria; often in conflict with Egyptians; known for their use of chariots as assault weapons

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

Hunters of Artemis    a group of maidens loyal to Artemis and gifted with hunting skills and eternal youth as long as they reject men for life

Hyacinthus    a Greek hero and Apollo’s lover, who died while trying to impress Apollo with his discus skills

Hypnos    the Greek god of sleep

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

imperator    a term for commander in the Roman Empire

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

Iris    the Greek goddess of the rainbow, and a messenger of the gods

Julian dynasty    the time period measured from the battle of Actium (31 BCE) to the death of Nero (68 CE)

karpoi (karpos, sing.)    grain spirits

kouretes    armored dancers who guarded the infant Zeus from his father, Kronos

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

Laomedon    a Trojan king whom Poseidon and Apollo were sent to serve after they offended Zeus

Lepidus    a Roman patrician and military commander who was in a triumvirate with Octavian and Marc Antony

Leto    mother of Artemis and Apollo with Zeus; goddess of motherhood

Lupercalia    a pastoral festival, observed on February 13 through 15, to avert evil spirits and purify the city, releasing health and fertility

Lydia    a province in ancient Rome; the double ax originated there, along with the use of coins and retail shops

Marc Antony    a Roman politician and general; part of the triumvirate, with Lepidus and Octavian, who together tracked down and defeated Caesar’s killers; had an enduring affair with Cleopatra

Marsyas    a satyr who lost to Apollo after challenging him in a musical contest, which led to Marsyas being flayed alive

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

Midas    a king with the power to transform anything he touched to gold; he selected Marsyas as the winner in the musical contest between Apollo and Marsyas, resulting in Apollo giving Midas the ears of a donkey

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    the half-man, half-bull son of King Minos of Crete; the Minotaur was kept in the Labyrinth, where he killed people who were sent in; he was finally defeated by Theseus

Mithridates    king of Pontus and Armenia Minor in northern Anatolia (now Turkey) from about 120 to 63 BCE; one of the Roman Republic’s most formidable and successful enemies, who engaged three of the prominent generals from the late Roman Republic in the Mithridatic Wars

Mount Olympus    home of the Twelve Olympians

myrmeke    a giant antlike creature that poisons and paralyzes its prey before eating it; known for protecting various metals, particularly gold

Nemesis    the Greek goddess of revenge

Nero    Roman emperor from 54 to 68 CE; the last in the Julian dynasty

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

Nike    the Greek goddess of strength, speed, and victory

Nine Muses    Greek goddesses of literature, science, and the arts, who have inspired artists and writers for centuries

Niobe    daughter of Tantalus and Dione; suffered the loss of her six sons and six daughters, who were killed by Apollo and Artemis as a punishment for her pride

nosoi (nosos, sing.)    spirits of plague and disease

nymph    a female nature deity who animates nature

Octavian    the founder and first emperor of the Roman Empire; adopted son and heir of Julius Caesar (see also Caesar Augustus)

Odysseus    legendary Greek king of Ithaca and the hero of Homer’s epic poem The Odyssey

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

omphalus    stones used to mark the center—or navel—of the world

Oracle of Delphi    a speaker of the prophecies of Apollo

Oracle of Trophonius    a Greek who was transformed into an Oracle after his death; located at the Cave of Trophonius; known for terrifying those who seek him

Ouranos    the Greek personification of the sky; father of the Titans

palikoi (palikos, sing.)    twin sons of Zeus and Thaleia; the gods of geysers and thermal springs

Pan    the Greek god of the wild; the son of Hermes

Pandora    the first human woman created by the gods; endowed with a unique gift from each; released evil into the world by opening a jar

Parthenon    a temple dedicated to the goddess Athena located at the Athenian Acropolis in Greece

Patroclus    son of Menoetius; he shared a deep friendship with Achilles after being raised alongside him; he was killed while fighting in the Trojan War

pegasus (pegasi, pl.)    a winged divine horse; sired by Poseidon, in his role as horse-god

Peleus    father of Achilles; his wedding to the sea-nymph Thetis was well attended by the gods, and a disagreement between them at the event eventually lead to the Trojan War; the guardian dragon at Camp Half-Blood is named after him

Persephone    the Greek queen of the Underworld; wife of Hades; daughter of Zeus and Demeter

phalanx (phalanxes, pl.)    a compact body of heavily armed troops

Phidias    a famous ancient Greek sculptor who created the Athena Parthenos and many others

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

Poseidon    the Greek god of the sea; son of the Titans Kronos and Rhea, and brother of Zeus and Hades

praetor    an elected Roman magistrate and commander of the army

Primordial Chaos    the first thing ever to exist; a void from which the first gods were produced

Prometheus    the Titan who created humans and gifted them with fire stolen from Mount Olympus

Pythia    the name given to every Oracle of Delphi

Python    a monstrous serpent that Gaea appointed to guard the Oracle at Delphi

Rhea Silvia    the queen of the Titans, mother of Zeus

Riptide    the name of Percy Jackson’s sword; Anaklusmos in Greek

River Styx    the river that forms the boundary between earth and the Underworld

Saturnalia    an ancient Roman festival celebrating Saturn (Kronos)

satyr    a Greek forest god, part goat and part man

shadow-travel    a form of transportation that allows creatures of the Underworld and children of Hades to use shadows to leap to any desired place on earth or in the Underworld, although it makes the user extremely fatigued

Sibyl    a prophetess

Sibylline Books    a collection of prophecies in rhyme written in Greek; Tarquinius Superbus, a king of Rome, bought them from a prophetess and consulted them in times of great danger

siccae    a short curved sword used for battle in ancient Rome

Sparta    a city-state in ancient Greece with military dominance

Stygian iron    a magical metal, forged in the River Styx, capable of absorbing the very essence of monsters and injuring mortals, gods, Titans, and giants; has a significant effect on ghosts and creatures from the Underworld

Talos    a giant mechanical man made of bronze and used on Crete to guard its shoreline from invaders

Tantalus    According to legend, this king was such a good friend of the gods that he was allowed to dine at their table—until he spilled their secrets on earth; he was sent to the Underworld, where his curse was to be stuck in a pool of water under a fruit tree, but never be able to drink or eat

Tartarus    husband of Gaea; spirit of the abyss; father of the giants; a region of the Underworld

Theodosius    the last to rule over the united Roman Empire; known for closing all ancient temples across the empire

Thracian    of Thrace, a region centered on the modern borders of Bulgaria, Greece, and Turkey

Titan War    the epic ten-year battle between the Titans and the Olympians that resulted in the Olympians taking the throne

Titans    a race of powerful Greek deities, descendants of Gaea and Ouranos, that ruled during the Golden Age and were overthrown by a race of younger gods, the Olympians

trireme    a Greek warship, having three tiers of oars on each side

triumvirate    a political alliance formed by three parties

Trojan War    According to legend, the Trojan War was waged against the city of Troy by the Achaeans (Greeks) after Paris of Troy took Helen from her husband, Menelaus, king of Sparta

Troy    a Roman city situated in modern-day Turkey; site of the Trojan War

Tyche    the Greek goddess of good fortune; daughter of Hermes and Aphrodite

Typhon    the most terrifying Greek monster; father of many famous monsters, including Cerberus, the vicious multi-headed dog tasked with guarding the entrance to the Underworld

Underworld    the kingdom of the dead, where souls go for eternity; ruled by Hades

Zephyros    the Greek god of the West Wind

Zeus    the Greek god of the sky and the king of the gods