Cross Island was depicted in Warcraft II as being a cross shaped peninsula on the southern shore of Lordamere Lake. It was the site where the Violet Citadel was situated, the Citadel itself being described as the capital city of the nation of Dalaran. The region was later attacked again when the Horde of Draenor invaded Dalaran in order to get the Eye of Dalaran.
The Last Guardian
In Warcraft III, The Frozen Throne, and World of Warcraft, Dalaran was depicted as coastal city-state with some close islands (including Fenris Isle) rather than being on a peninsula. Cross Island is not mentioned either in the novel Beyond the Dark Portal.
In The Frozen Throne, the northwest portion of Cross Island may possibly be visible in two of the level maps (Misconceptions and A Dark Covenant). Though Dalaran is on a lake-shore and not an island, it still seems to have remained cross-shaped, with the southern waters being reduced to a moat. It is possible that the southwest portion of the former island was seen during Under the Burning Sky, the southern portion was seen during The Siege of Dalaran, and the southeastern portion was seen during The Ruins of Dalaran.