In Irish mythology, Cían (, "long, enduring, far, distant"), also known as Scal Balb, son of Dian Cecht of the Tuatha Dé Danann, is best known as the father of Lug. In most versions, Lug's mother is the Fomorian princess Ethniu, but in some versions Cian is also known as Ethlend, hence Lug is known as Lug mac Ethlend.
In the saga Cath Maige Tuired Cian's union with Ethniu is a dynastic marriage following an alliance between the Tuatha Dé and the Fomorians. In the Lebor Gabála Érenn Cian gives the boy to Tailtiu, queen of the Fir Bolg, in fosterage.
A folktale told to John O'Donovan by Shane O'Dugan of Tory Island in 1835, has a hero named Mac Cinnfhaelaidh, but since the story has been taken as a version of the birth of Lugh, and was adapted as such by Lady Gregory, Mac Cinnfhaelaidh has been identified as Cian. In this tale, Balor, king of the Fomorians, hears a druid's prophecy that he will be killed by his own grandson. To prevent this he imprisons his only daughter in the Tór Mór (great tower) of Tory Island, cared for by twelve women, who are to prevent her ever meeting or even learning of the existence of men. On the mainland, Mac Cinnfhaelaidh owns a magic cow who gives such abundant milk that everyone, including Balor, wants to possess her. While the cow is in the care of Mac Cinnfhaelaidh's brother Mac Samthainn, Balor appears in the form of a little red-haired boy and tricks him into giving him the cow. Looking for revenge, Mac Cinnfhaelaidh calls on a leanan sídhe (fairy woman) called Biróg, who transports him by magic to the top of Balor's tower, where he seduces Eithne. In time she gives birth to triplets, which Balor gathers up in a sheet and sends to be drowned in a whirlpool. The messenger drowns two of the babies, but unwittingly drops one child into the harbour, where he is rescued by Biróg. She takes him to his father, who gives him to his brother, Gavida the smith, in fosterage.
Cían was killed by the sons of Tuireann, Brian, Iuchar and Iucharba, after trying unsuccessfully to escape from them in the form of a pig. Lug set them a series of seemingly impossible quests as recompense. They achieved them all, but were fatally wounded in completing the last one. Despite Tuireann's pleas, Lug denied them the use of one of the items they had retrieved, a magic pigskin which healed all wounds. They died of their wounds, and Tuireann died of grief over their bodies.