"The Circular Ruins" (Spanish: Las ruinas circulares) is a short story by Argentine author Jorge Luis Borges. First published in the literary journal Sur in December 1940, it was included in the 1941 collection The Garden of Forking Paths (Spanish: El jardín de senderos que se bifurcan) and the 1944 collection Ficciones. It was first published in English in View (Series V, No. 6 1946), translated by Paul Bowles. Since publication, it has become one of Borges's best-known stories.

The story is about a man who gradually dreams another man into existence in the ruins of an ancient temple. Though he is successful, the dreamer realizes at the story's conclusion that he himself is someone else's dream. Critics have interpreted "The Circular Ruins" as exploring themes of philosophical idealism, Gnosticism or kabbalism, and creativity.

A man arrives by canoe at the burned ruins of an ancient temple. The temple is centered on the statue of an ambiguous deity that appears to be a tiger or a horse. The man immediately falls asleep; his goal, the narrator reveals, is to "dream a man with minute integrity and insert him into reality." Local villagers bring the man food, and he spends most of his time sleeping in the ruins.

At first, the man dreams that he is addressing a group of pupils on anatomy, cosmography, and magic; he hopes to find among his pupils "a soul which would merit participation in the universe." The man eventually narrows the group of students down to a boy who resembles him, but soon finds himself stricken with insomnia and unable to continue dreaming.

After taking a rest to regain his strength, the man attempts a different tactic: he begins to dream a man piece by piece, beginning with his heart and slowly adding other organs and features. The process takes over a year and is painstaking. Frustrated, the man consults the temple's deity, which in a dream is revealed to be a multifaceted deity known as "Fire" that also can appear as a bull, a rose, and a storm. Fire promises the man that he will bring the dreamed one into reality, and that everyone but Fire and the dreamer will believe the conjured man to be flesh and blood. Fire demands that after the conjured man's education is finished he be sent to another ruined temple downstream "so that in this deserted edifice a voice might give glory to the god."

The man spends two years instructing the conjured man, whom he comes to view as his son. Though he secretly dreads their separation, the man eventually sends his son to the second temple. Before he does so, though, he destroys his son's memory of his apprenticeship, "so that he would never know he was a phantom, so that he would be thought a man like others".

The man remains at his temple and hears word from travelers of his son, who is reportedly able to walk on fire without being burned. Though the man still worries his son will find out his true origins, his fears are interrupted by a forest fire that emerges from the south and envelops the ruined temple. Accepting death, the man walks into the flames. He feels no pain and realizes "with relief, with humiliation, with terror" that he too is an illusion, and that someone else is dreaming him.

The Circular Ruins deals with themes that recur in Borges's work, particularly idealism and the manifestation of thoughts in the "real world".