The large nebula known as the Roil was located in the Gordian Reach sector, a part of the Trans-Hydian portion of the Outer Rim Territories. It was situated between the hyperlanes known as the Junction-Tierell Loop and the Wetyin's Way spinward and the Ardan Cross and the Feena Run in the trailing direction. Southward, the vast cloud extended to the Maridun system. The nebula served as a dividing line between the Loop Worlds and Back Reach areas of its sector.
The Roil consisted of garish, many-colored dust and gas. The world Arkuda in the nearby Arkuda system was known for its spectacular nighttime skies, and the Cometwash, a blue giant–type star orbited by swarms of comets in the star system of the same name that was located at the Roil's edge, was likewise famous for the sights it offered to visitors.
A stellar nursery, the Roil contained clumps of young blue and white stars. The fringes of the nebula were also the site of the knot of proto-stars known as the Vallusk Cluster. It was nearly impossible for starships to navigate through the Roil; an exception was the hyperspace route known as the Korphir Trace, which passed through the nebula at its southern section and connected the Arkuda and Korphir systems, serving as the only connection between the Loop Worlds and the Back Reach.
For centuries prior to the end of the existence of the Galactic Republic, which transformed into the Galactic Empire in 19 BBY, the natural barrier posed by the Roil was exploited by privateers from the world Korphir, who preyed upon shipping along the Junction-Tierell Loop before returning to Korphir via secret routes through the nebula.
The Roil was introduced in the 2009 reference book The Essential Atlas, authored by Daniel Wallace and Jason Fry, which placed it in grid squares Q-5 and Q-6. Beside the Roil, the map of The Essential Atlas illustrating the Gordian Reach also depicted the Denarii Nebula, and Fry later noted that, when creating that map, the book's chief cartographic illustrator, Modi, had complained about Fry's insistence that all maps of the work feature nebulae.
- The Essential Atlas