Black soup was a dish in the cuisine of ancient Sparta, made with boiled pork meat and blood, using only salt and vinegar to flavour. The soup was well known during antiquity in the Greek world, but no original recipe of the dish survives today. The earliest recorded mention of the soup can be dated to the fifth century BC, in a comedy titled The Miners, written by Pherecrates. The ancient sources provide contradictory accounts on whether the soup was a luxurious meal served only at banquets or a dish that could be afforded by all Spartiates. Throughout history, black soup has been praised by and associated with figures such as Benjamin Rush and Adolf Hitler, although Hitler was (debatably) vegetarian.

The ancient Greek author, Plutarch, who wrote in the first and second century AD, mentioned a Spartan dish in his Life of Lycurgus named μέλας ζωμός, mélas zōmós. Today, the phrase has been translated to "black soup" or "black broth". In other ancient sources, this same dish was also known as αἱματία, haimatía, which means "blood soup", and βαφά, bapha, which can be translated as "dip sauce". Other times, this dish was simply referred to as ζωμός, zōmós.

In Ancient Greek, the term μέλας, mélas means black, while ζωμός, zōmós could refer to any soup cooked using animal products. The 1st-century AD medical writer Dioscurides recorded that there were many variations of zomós. For example, it could be cooked using frog, crayfish, rooster, beef, deer fat, and fish. The 5th–4th-century BC philosopher Plato also used the term zōmós when referring to a meat dish. Aristotle, writing around the 4th century BC, stated in his Historia Animalium that zōmós could be made using horse, pork, mutton, or goat. Contrarily, the ancient Greeks had another designated name for soups made primarily with vegetables, which was ἔτνος, étnos.

The majority of the ancient sources that describe black soup were written by non-Spartan authors. These authors include Pherecrates of the fifth century BC, Alexis and Matro of Pitane of the fourth and third century BC, Nicostratus of the fourth century BC, and Euphron of the third century BC. For example, in Pherecrates' comedy, The Miners, a woman returning from the underworld states that she saw black broth free-flowing through the streets. Antiphanes, a contemporary comedian of Alexis, had also noted that black soup was a staple of the Spartan culture in a play titled The Archon. A fragmentary anecdote indicates that Nicostratus once ridiculed a cook for not knowing how to prepare the Spartan black soup, along with other dishes such as "thríon" (θρῖον: stuffed leaves), "kándaulos" (κάνδαυλος: a Lydian dish), and "mattýe" (ματτύη: a type of dessert).

Other references to black soup are indirect. For example, in Aristophane's Knights, one of the lines in this comedy is "He has had tasty stews exported from Athens for the Spartan fleet." Although the reference is not explicit, the fifth century BC poet was suggesting that the Spartan version of stew was not as good as the stew cooked by the Athenians. Classics scholar David Harvey stated that the playwright was likely making fun of Spartan black broth in this passage.

Suda Lexicon, a Byzantine Greek historical encyclopedia compiled much later during the tenth century AD, states that zomós was a stock cooked using pig, cow, goat, sheep, or bear meat. Julius Pollux's lexicographic work, Onomasticon, notes that the black broth was a Spartan dish cooked with meat and blood.

According to what Euphron (a third-century BC comedy poet) had written in one of his fragmentary comedies, titled The Brothers, a cook mentions that a man named Lamprias was responsible for inventing the Spartan black soup. However, this claim would be impossible to verify today.

No recording of black soup's exact recipe exists today. Ancient literary sources, including historical, medical, and lexicographic, contain descriptions of black soup and its ingredients. Through interpreting these sources, it can be concluded that the Spartans cooked this dish using pig's blood and meat, with salt and vinegar as the only condiments. According to Plutarch's descriptions, the solid meat chunks in the soup were to be taken out and served separately to the younger attendees during banquets.