Obsolete

In the Civilization series, an obsolete unit, city improvement, resource, and/or wonder is one whose function has been surpassed or replaced by technological development. Generally, obsolete units can no longer be produced, while improvements, resources, and wonders cease to provide their effects. Obsolescence applies as soon as the civilization obtains the necessary technology; in several games, Wonders become obsolete regardless of which civ first acquires the tech.
Most games allow obsolete units still in the field to be upgraded to newer classes for a variable gold cost.
== Sid Meier's Civilization and Civilization II ==
* When a unit becomes obsolete, it is removed from the list. Units already in production are not removed until the build order changes.
** In Civilization II, obsolete s are automatically upgraded to their replacement in . also provides its host free upgrades to every unit in the field for as long as it is active; such units will lose cy where applicable.
* are the only that can become obsolete: and remove the civilization's existing Barracks from all cities. Barracks under construction remain in production, and replacement Barracks can be built; these have increased costs.
** In Civilization II, are rendered obsolete by and . Unlike in Sid Meier's Civilization, they are sold off rather than deleted and the treasury is reimbursed.
* Wonders are rendered obsolete when any civilization discovers the appropriate advance. The wonder's bonus stops, but the wonder itself remains in its host city and continues to contribute to the civ's . Unbuilt obsolete wonders remain available for construction, denoted by an asterisk (*).
== Civilization III ==
Unit obsolescence behaves similarly to Civilization II, with two important changes:
* automatically upgrades to the newest unit based on the 's available resources (e.g., a civilization that has researched but does not have access to will produce Riflemen instead of ).
** If a city loses access to a required resource during production, the unit will be completed, but the build order will fall back to its closest available precursor in the next production prompt.
* Existing units can be manually upgraded when stationed in a city with the appropriate improvement for their domain ( for , for , and for ) for a cost based on the difference in production cost. halves this cost, and does not expire.
* Additionally, any unit that is flagged to start a (i.e., s) will remain available to build, even if superseded by newer units, unless/until the civ has celebrated a Golden Age.
Wonders expire only when their host civilization discovers the appropriate advance. Obsolete wonders are removed from the production menu, and incomplete wonders will prompt a change to the build order.
s and s do not expire in the base game, but can be modded to do so.
== Civilization IV ==
=== Units ===
 obsolescence behaves similarly to Civ3: an obsolete unit will automatically in the 's queue without loss of hammers, provided it has access to all necessary s. Existing units can be upgraded anywhere within the civ's for a cost proportionate to the difference in production cost.
=== Resources ===
Obsolete s continue to provide their tile yield, but the civ no longer accrues its associated trade resource, and all are cancelled. The civ can still import the resource, however. Resources that can become obsolete include:
* (with )
* (with )
* (with )
=== Buildings and wonders ===
Obsolete wonders and buildings are immediately removed from the build order, and all invested hammers are lost. Existing buildings are not removed, and continue to provide output and prerequisites for other production items (e.g., obsolete Walls still enable construction of Castles, and Monasteries will continue to allow recruitment of Missionaries). All other output modifiers, such as and points, are nullified.
Buildings that can become obsolete include:
* , (with )
* (with )
* , , , (with in Beyond the Sword, or in vanilla)
* , (with )
* , (with )
Wonders that can become obsolete include:
* (with )
* (with )
* (with )
* (with )
* (with )
* (with )
* (with )
* (with )
* (with )
* (with )
* (with in Beyond the Sword, or in vanilla)
* (with )
* (with )
== Civilization V ==
 obsolescence behaves similarly to Civilization IV. Obsolete units in production will automatically upgrade without losing any invested , provided this will not create a deficit in the civilization's strategic resources. Likewise, existing units can only be upgraded if surplus resources are available (where required).
s and wonders do not become obsolete, with the exception of the (with ).
== Civilization VI ==
 obsolescence behaves similarly to Civilization V. Obsolete units in production will automatically upgrade to their direct replacement without losing any invested , provided this will not create a deficit in the civilization's s. For example, the becomes obsolete with , since this enables the , the next melee unit.
s can also become obsolete as the player develops more advanced s, replaced by new cards with more -appropriate effects.
s, s, and s do not become obsolete, although , , and can no longer be built after is researched and cease to provide defensive bonuses.
== Sid Meier's Alpha Centauri ==
 and s are not subject to obsolescence. Depending on the player's game settings, s will automatically be flagged obsolete as new components become available; they will no longer appear in the base menu, but remain accessible in the . The player can flag and unflag obsolescence at will.
Units can also be retired, deleting the design from the workshop. This is a manual order by the player. Any units currently in the field will be instantly disbanded.
Category:Game concepts