The Celts are an offensive civilization that focuses primarily on infantry and siege weapons, but they also have decent cavalry and navy as well. While the Celts fare better than most civilizations in early games, they are the most powerful from Castle Age and onward. Thanks to a number of non-situational bonuses and units, the Celts are ideal for new players and experts alike.
Their infantry move faster than those of other civilizations and their unique unit, the Woad Raider, is the fastest infantry unit in the game. They also have access to all siege weapons which offers a faster attack speed. However, they lack the ability to develop gunpowder units such as the Bombard Cannons. In addition, their unique technology, Furor Celtica, greatly increases the hit points of their siege weapons, making them quite difficult to destroy. They also fare better economically since their lumberjacks can gather wood faster than those of other civilizations. This frees up some population space since fewer villagers have to be tasked to gather it. In addition, their herdables cannot be stolen as long as it is within the line of sight of any Celtic unit, while they can steal herdables of other players with their units.
Defensively they are average, lacking many defensive upgrades, especially Architecture, and Bombard Towers. Their cavalry is decent but is nothing special since they lack Bloodlines. They are able to upgrade to Hussar and Paladin, but they lack Camels. However their lack of camels is compensated by the faster speed of their Spearmen. They also have poor Monks, missing many technologies at the Monastery. Their archers are also incredibly weak, lacking the Arbalest upgrade, the lack of Bracer, and the lack of Thumb Ring.
Celts have a strong early-game economy due to their Lumberjack bonus. They have a powerful Dark Age rush (drush) because their Militia move faster than opposing Militia and Villagers, allowing them to perform hit-and-run tactics, and raid more effectively. This bonus lasts into the Feudal Age and beyond, as it essentially gives them free Squires plus a little bit more, giving them an advantage running from or pursuing other infantry.
In the Feudal Age, Celts can do more or less whatever they want, although Infantry are the go-to option since they keep their value even in the later ages. Lingering in the Feudal Age is generally a bad idea, since Celts really shine in the Castle and Imperial Age. Celtic Siege is among the best in the game, with extra health and faster firing rate. Woad Raiders make great raiding units due to their speed and attack bonus against buildings, and Halberdiers are good for protecting Siege, since they are better equipped to keep up with Cavalry than other civilizations because of the speed bonus. The Lumberjack bonus is fabulous for getting extra wood to make Siege Engines as well. A Celt player must be sure to keep multiple Siege Workshops up (preferably at least four) since Siege is slow to create.
The Celtic Lumberjack bonus also helps with naval conflict, allowing them to make more ships with fewer Villagers. Celts have a good navy, only missing Fast Fire Ship and Elite Cannon Galleon, neither of which are vital to succeed.
Being the official tutorial civilization, the Celts are recommended for newer players due to the Celts being a straightforward civilization with strong synergy with their civilization bonuses (faster woodcutting rate, faster firing and producing siege), their unique tech, and an infantry bonus with an infantry unique unit. Their tech tree is also well-rounded with strong siege and infantry and a decent cavalry and navy, with archers and defense being their only clear weakness.
Celtic defenses in The Forgotten are greatly improved with their new Castle Age unique technology, Stronghold, that increases the firing rate of Towers and Castles. Despite so, they still lack Architecture and Bombard Towers, though this new improvement make their defense better. Although Furor Celtica now gives only 40% HP to siege weapons, the amount is still significant enough in the battlefield. If playing alongside with the Koreans, the minimum range for Celtic Mangonels are eliminated. This combining with the faster fire speed makes Celtic Mangonels among the most feared siege unit in the game.
As all civilizations received the new siege unit at their siege Workshop the Siege Tower and the Celts being one of the civilizations that favors the use of units of this kind, the addition of the new unit make a great difference as in the Celts case they are spammed quicker, and with Furor Celtica they will have more hit points making this unit more resilient against enemy attacks especially from towers behind a wall since the purpose of the siege tower is only leaving foot troops in the other side of the wall and the ability of this tower also synergize nicely with the infantry bonuses the Celts have.
Celts should be paired with civilizations that rely heavily upon their siege workshop units, such as the Slavs, Koreans, Mongols, and, particularly Ethiopians (with their own Torsion Engines upgrade) and Khmer (with their own Double Crossbow upgrade). The Celtic team bonus helps them keep up a faster and more steady supply of siege units.
Celts benefit from allies such as the Goths, who enable them to train their infantry faster, and from Koreans, because of the reduced minimum range for Mangonel units. The Italian Condottiero is also very useful for the Celts, because it can reach and counter dangerous gunpowder units very quickly. Alternatively, Genitours from Berber allies will also be the saving grace for feeble Celtic missile continents against archer-oriented civilizations, together with Kasbah upgrade to make mass-producing Woad Raiders and Trebuchets in quicker speed possible. Slavs team Bonus will also enable Celt to save some wood in houses, and invest that wood on more siege units. Khmer allies also proved to have good synergy with the Celts, not only contribute Hand Cannoneers for gunpowder support, they also grant Celtic Scorpions adequate range boost, in exchange for quick production speed of their own counterparts and Ballista Elephants, both enhanced by Siege Engineers and Double Crossbow technologies, as "friendly-fire-free" counter-measures against archers, ships and massed units.
The Vietnamese are also a good ally for the Celts: even in the Dark Age, they can reveal exact locations of the enemy bases at the beginning, allowing the Celtic players to unleash surgical Militia rushes rapidly. As the game comes to the Imperial Age, by granting the Vietnamese competitive siege and cavalry support by Hussars,Paladins, speed-enchanced infantry like Woad Raiders, plus an assortment of advanced non-gunpowder siege weapons also enhanced by Siege Engineers and Furor Celtica, the Celt players can receive extra aids in return: gold subsidy for extra Woad Raiders and siege weapons from Paper Money, extra fire support from Imperial Skirmishers to pick off hostile archers and Halberdiers, thus paving the way for the Celtic cavalry charges, or their late-game dominance as gold resources become scarce.
The Woad Raider having fast movement speed can raid effectively enemy towns, and catch and destroy enemy siege units so civilizations with poor defenses such as Goths and Magyars, and civilizations reliant on siege Weapons may have trouble against them. They are also useful against archers as they can dodge arrows so civilizations like Britons and Vietnamese will have troubles against them.
As their Halberdiers move faster they are better suited to counter cavalry as they can engage them so cavalry based civilizations will also have trouble against Celt Halberdiers, Franks, Magyars, Huns and Persians will have a harder time dealing against Celtic Halberdiers. This also gives the Celts an advantage at trash wars especially against civilizations that doesn't have fully upgraded Skirmishers (like the Turks) or good Champions (like the Persians).
As their Militia line moves faster and have good economy they have an advantage in open maps against civilizations with bad early game like Turks, Spanish, Portuguese and Khmer as they can raid since the Dark Age. This also gives the Celts a second Advantage at Trash Wars as the Champion is considered a counter to almost all Trash units, as well as being better suited to also counter siege units like their castle counterpart the Woad Raider.
Since all their siege workshop Siege Weapons are bulkier, spam faster and fire faster they have a huge advantage against civilizations with poor defenses (like Goths and Magyars), even civilizations with Good Defenses Like the Incas, Teutons and Byzantines will have a harder time against the Celtic Siege Line. Also as the onagers are a counter to masses of archers and densely packed slow moving units, civilizations that either rely on archers (like Mayans, Vietnamese and Britons) or civilizations that rely on masses of units (like Malay and Goths) will have trouble against Celtic Onagers, similar logic can apply to their bulkier Rams when facing archers and with Scorpions when facing masses of infantry. As Onagers can cut trees these advantages also can apply in maps with dense Forests Such as Arena and Black Forest.
Defensively they are at an advantage against civilizations with a mediocre siege workshop or proper anti-building units thanks to the Stronghold Technology (without considering the Trebuchets which every civilization has access to). This includes Britons, Berbers, Japanese and Magyars (of course once they get to Imperial this advantage is no longer a problem for them).
Regarding naval Warfare they are at an advantage against civilizations with a poor early game navy as their lumberjack bonus enables the Celts to acquire wood fast enough to make a sizable navy early in the game. Even civilizations like Byzantines, Koreans, Persians, and Portuguese may have trouble in the early game against Celts in naval encounters as most of their naval bonuses start later.
Though the Woad Raider is a fast enough unit that can dodge arrow-fire, if the player forgets to micro them they can be overcome by archers that have reached a critical mass, so Britons, Vietnamese and Chinese players should take this into consideration. They also struggle against Heavy cavalry (prominent cavalry civilizations like Franks, Persians, Spanish and Malians can counter with ease an army composed of Woad Raiders) so any Celt player must not forget to pair their Woad Raiders with Halberdiers.
Since they don't get access to any kind of gunpowder unit aside from petards, the Cannon Galleon and Demolition ship they fare poorly in the late game against civilizations that fare otherwise like Turks, Portuguese and Spanish, especially if the game starts at Castle Age onwards, this is especially true for the civilizations that have access to the Hand Cannoneer as they can counter infantry and the civilizations that can access Bombard Cannons as they can Counter Onagers and Scorpions from a safe distance. Sometimes this disadvantage can also be exploited in closed maps like Black Forest against Celts as late game civilizations can build up their way to Imperial Age if they manage to wall up in the early game and survive.
As their infantry relies on movement speed to get an advantage and not on brute force, numeric superiority or resilience they may fell apart against other prominent infantry civilizations like the Aztecs (which their infantry have more attack and also have the Jaguar Warrior as a counter for infantry) The Vikings (which have bulkier infantry), Malays (which their gold free Two-handed swordsmen and Karambit Warriors can outnumber the Celtic infantry), The Japanese (which their infantry attacks faster and also the Samurai can counter with ease the Woad Raiders) and Slavs (which their infantry can deal trample damage after researching Druzhina)
Byzantine Cataphracts counter the Celts almost perfectly, as they are too dependent on infantry and Siege and are limited in the ways they can counter them (aside of their Halberdier which still have problems countering Cataphracts and the Heavy scorpions if the Celts massed them) these because their bonus damage against infantry and the fact they can catch siege engines being a cavalry.
Large contingents of Mayan Plumed Archers or Incan Slingers can be a problem for the Celts if they don't make use of skirmishers.
Mayans, Incas and Aztecs have access to the Eagle Warriors that can counter very effectively siege units. Similarly civilizations with access to good Light cavalry can be a huge threat to Celtic Siege units such as Magyars (that also their unique unit deal bonus damage against siege units) Mongols (that not only have good Hussars but also their unique unit the Mangudai deal bonus damage against siege units) and Huns.
Despite the fact that their lumberjack bonus indirectly helps in naval encounters this advantage may be short lived as this also means they deplete the wood on the islands they control faster. Also they lack Fast fire ships, Elite Cannon Galleons and Bracer. So civilizations with either late game sustainable economy (like Malay and Portuguese both of which have infinite resource bonuses) or civilizations that furthers up the statistics of their navy or have access to unique ships (like Byzantines, Chinese, Berbers, Portuguese and Saracens for the first and Koreans, Vikings and Portuguese for the last) can overturn them at the late game.
Despite the Stronghold Technology helps out the Celts to defend in the Castle Age, Civilizations with good siege engines especially good bombard Cannons and Trebuchets can overturn that advantage at Imperial Age as Celts lack several defensive upgrades, these civilizations include Ethiopians, Turks, Portuguese, Huns, Britons and Japanese.
Celts have mediocre archers so this also limits the responses they may have against Infantry based civilizations.
Celts have a clear advantage in any densely forested map (like Arena, Hideout, Black Forest and Oasis) as their lumberjacks work faster while at the same time having Onagers that fires faster enabling them to make paths faster through the forest that enables them to take their enemies by surprise. Considering also their Onagers there is a very rarely seen strategy in open maps like Arabia that consist in using the Onagers to clear out any patch of forest an opponent may take for themselves neglecting them the access to wood while the Celt player himself can get their wood fast, this particular strategy is more effective for the Celts if starting in Castle Age onwards.
Their stealing sheep bonus is more useful if playing in maps in which players can find more sheep than the usual eight around the starting points, these include Ghost lake, Oasis, Yucatan and Nomad, this is even more advantageous if playing with revealed map as they can find faster the initial locations of their rivals to steal their sheep.
In regicide mode they get an advantage as they manage to research Stronghold early for defend their initial location better. As well as getting an advantage in Fortress map as Stronghold also benefits towers and in that map there are several towers pre-deployed, this also considering in Fortress each player also starts with a barracks enabling Celts to amass their infantry since the beginning of the match.