vulnerability to cold. Drakes are the most maneuverable faction, though their size makes them prone to attack in most terrain. The exact units used by the factions, and the faction names, change based on the era or the campaign. The above are the factions of the "Default" era, which is the most played one on the multiplayer servers, and its extension "Age Of Heroes". There are also a number of user-created factions, several of which are grouped together in downloadable "Eras." For example, the Imperial Era includes the Roman-influenced Lavinians, the Marauders, and the Wild Elves, featuring completely new unit trees and abilities. An alternative era, which contains the Islam-influenced faction Khalifate, was integrated (as of 6 January 2014) in the official development line, Wesnoth 1.11.8, tested to become part of the mainline version. However, it is quite possible to create factions that can be used in the default eras, though the amount of blessing given by the creators for each may vary. Campaigns The stable version of The Battle for Wesnoth comes with 17 single-player campaigns, each of which has various difficulty levels. More user-authored campaigns can be obtained in the form of add-ons stored on Wesnoth's campaign server, and these are sometimes mainlined as official campaigns. The original campaign for The Battle for Wesnoth was "Heir to the Throne", a campaign with 23 gameplay scenarios where Konrad, a young heir to the throne of Wesnoth, allies with rebellious elves and other races to claim the throne from the usurper queen Asheviere, her loyalist army, and her orcish mercenaries. Characters from "Heir to the Throne" are protagonists in campaigns such as "Legend of Wesmere" and "Delfador's Memoirs". Other campaigns feature different factions, like the dwarves in "The Hammer of Thursagan" or "Northern Rebirth" or "Sceptre of Fire", the loyalist army of Wesnoth in "The South Guard" or "The Eastern Invasion", and undead in "Descent into Darkness" or "Secrets of the Ancients". Even mermen can be played in "Dead Water", or orcs in "Son of the Black Eye". Finally, "Under the Burning Suns" is set in the distant future, long after the time of the other campaigns, featuring elves who fight better during the day. A multiplayer campaign titled "World of Conquest" is added to the game on version 1.16 after previously being an unofficial add-on. Unofficial campaigns Many official campaigns were only user-made add-ons, for example "An Orcish Incursion",