Before designing the block, Mark Rosewater gave Shawn Main the task of compiling a booklet in order to catalog how Magic has used Greek mythology in the past.
While the block has representatives of four of Magics iconic creature types (Demon, Dragon, Hydra and Sphinx), the white representative is missing as Angels are not a part of Greek mythology. Their role has been taken over by Archons for the set.
The city of Akros is modeled after the city of Sparta, said to be centered around a more rough and unforgiving lifestyle and known for its warriors. The city of Meletis is modeled after Athens, often thought of as a more civil and refined society. The city of Setessa is styled after the Amazones, focusing on female warriors while men are expected to wander and find their place elsewhere.
The Theriad, an epic story from which excerpts are given through flavor text throughout the block, is a close analogue to the ancient Greek epic poem The Iliad, traditionally attributed to Homer circa 1260 BC.
Theros was almost a block that jumped thousands of years between sets. The idea was killed because the creative team didn't have the resources at the time to pull it off.
Sip of Hemlock depicts a real-world form of execution in ancient Greece, in which the prisoner would be forced to drink an extract of hemlock. A famous person that was executed this way was the philosopher Socrates.
Titan of Eternal Fire and Chained to the Rocks both refer to the story of Prometheus, a titan that give the gift of fire to the Humans and was punished by the gods for it. His punishment was being chained to a rock face for eternity, with a bird eating the liver out of his body every day.
Titan's Strength depicts a person having to push up a boulder up a hill, similar to the legend of Sisyphus who was punished with this futile task as the boulder inevitably would roll down the hill, forcing Sisyphus to start over.
The activated ability on Bow of Nylea is meant to represent the four seasons. Each result also refers to a number, which increases from 1 to 4 within it.
Underworld Cerberus is a more literal interpretation of the mythical creature of Cerberus, a three-headed dog who guards the gates of the underworld. Mechanically there must be a blocker for each head, while the card is on the battlefield the graveyard cannot be accessed, but when the Cerberus is slain all the dead can escape the underworld.
Akroan Horse mirrors the Trojan Horse, a trick in which warriors infiltrated the city of Troy inside a wooden horse that was offered to their enemies.
Gild is a reference to the tale of King Midas, who had the ability to turn everything he touched (hand wise) into gold.
Impetuous Sunchaser is an analog to the tale of Icarus who, with his father Daedalus, created wings from bird feathers and wax. Icarus became overly confident in this invention and plummeted to his death after flying too close to the sun, causing the wax in his wings to melt.
Weight of the Underworld references the myth of Sisyphus who was punished for his self-aggrandizing craftiness and deceitfulness by being forced to roll an immense boulder up a hill only for it to roll down when it nears the top, repeating this action for eternity.