Camelot seems to be a relatively late addition to Arthurian legend. By the 12th century most works placed Arthur's court in Caerleon. Camelot first appears in "Lancelot, the Knight of the Cart" (1170s) by Chretien de Troyes. The poem holds the distinction of being the first where Lancelot is the protagonist. Its theme of featuring an adulterous affair between Lancelot and Guinevere was also a first in Arthurian legend. the works of de Troyes still have Caerleon as the main seat of power for Arthur, but have Arthur traveling around his kingdom and holding court at different locations. Camelot receives a brief mention as the location where Arthur celebrated Ascension Day (the ascension of Jesus to the Heavens). 
 
The Vulgate Cycle (1210s - 1230s), a series of five volumes, provided a long unified account of the Arthurian legends. It begins with Joseph of Arimathea bringing the Holy Grail to the island of Great Britain (vol. 1). It continues with the life of Merlin and Arthur's early years (vol. 2). Then features the adventures of Lancelot and his affair of Guinevere, along with other tales of the Knights of the Round Table (vol. 3). Followed by the Grail Quest (vol. 4) and ending with the death of Arthur at the hands of Mordred and the collapse of his kingdom (vol. 5). Camelot is featured here as an early seat of Christianity in Britain, the location of the  Arthur-Guinevere marriage and the principal city of Arthur's realm.  
 
The work seems to have received an answer in the so-called Post-Vulgate Cycle (1230s-1240s), a series of four volumes, which reworked the material of the Vulgate Cycle to de-emphasize love affairs and earthly matters and emphasize on spiritual aspects. Significant differences include an emphasis on Mordred being the result of an incestuous  affair and a connection between the Lady of the Lake and the sword Excalibur (details absent in the Vulgate Cycle), the introduction of themes and characters from the Tristan cycle and the Grail Quest being a spiritual quest above all. Among the things remaining from the previous work is Camelot's role as the seat of power for Arthur. 
 
Arthurian works from the 13th to the 15th century seem to follow different literary traditions. French and other continental European works are influenced by the Vulgate and Post-Vulgate cycles, featuring Camelot frequently. Most Welsh or English works of the same period place Arthur's court still in Caerleon or in Carlisle (Caer Luel/Caer Llewelyn). A major exception is "Sir Gawain and the Green Knight" (late 14th century), a work written in Middle English and rich in medieval symbolism. There the court of Arthur is placed in "Camylot" (sic). 
  
"Le Morte d'Arthur" (1450s - 1470s, published 1485) by Thomas Malory ends the parallel traditions. Mallory drew both from the continental and British Arthurian traditions to complete his major work.  William Caxton, his publisher, divided it into 21 volumes, 507 chapters. Covering tales from the birth to the death of Arthur, the full work gives a somewhat pessimistic look on the Arthurian figures and chivalric society. Arthur, Lancelot and the other knights consistently try and fail to live up to their chivalric codes, chaste courtly love is replaced by   lustful affairs and passion overcomes reason. Arguably Mallory was influenced by the Wars of the Roses (1453 - 1487), the bloody civil war fought in England, Wales and Ireland of his time. The departure is that Camelot itseldf becomes the center of much of the action. 
 
Since Malory's work was arguably the last major Arthurian work of the Middle Ages, almost all later depictions of the legend would draw heavily from it. Camelot would eclipse all other locations of the Arthurian legend from the popular imagination. A question often asked in later times would be "where is/was Camelot?". The answer is not that easy.   
 

• The name may derive from Camulodunum (modern Colchester), a significant location of early Roman Britain. It figures prominently in Roman accounts but was destroyed by Boudica c. 60 AD. The city seems to have been rebuilt by the 8th century and called "Caer Colun" by Nennius.  
• Several descriptions of Camelot have it  surrounded by plains and forests. This may derive from Celliwig (forest grove), a capital of Arthur in Welsh legend. Celliwig  was typically placed in Cornwall.      
• *Some of its features such as "impressive architecture and many churches" were probably transferred from accounts about the glories of Caerleon and Carlisle in other Arthurian works. 
•  "Thomas Malory firmly identified Camelot with Winchester. Winchester was the capital of the Anglo-Saxon kingdom of Wessex . The native dynasty unified what is known as the Kingdom of England in the 10th century. Winchester was still the capital to the Norman Conquest of 1066. A 13th century Round Table in Winchester was rumored to be the Arthurian Round Table by the time Malory wrote his work. Arguably making it ideal for the ancient seat of power Malory had in mind. 
• William Caxton scoffed at the notion of Camelot being outside Wales. He pointed to the prominent ruins of Camelot in Wales. His description is thought to point towards Caerwent. A Roman trading center, it seems to have had served as a major city from the 4th to the 9th century. It served for a while as capital to the Kingdom of Gwent. The main church of Caerwent was dedicated to Saint Stephen. So was the main church of Camelot described by Malory and other works. 
• A theory favored in Tudorian England associated Camelot  with Cadbury Castle in Somerset. 20th century excavations located there a hill fort which was in use from the 470s to the 580s. Artifacts from the eastern Meditteranean point to wide trade links for the location. Archaeologists theorise that it was a seat of power for a major Brythonic ruler, perhaps a prince of Dumnonia (4th-8th century Kingdom).  
• The location of Slack, West Yorkshire seems to have been called Camulodunum during the Roman era. Since it has the name association with "Cam" but was still outside Saxon rule in the 6th century, it has been argued as more likely than Colchester to be the seat of a Celtic ruler.  
• Tintagel Castle in Cornwall has been suggested as "Camelot". The supposed birthplace of Arthur and later a seat to rulers of dumnonia, it has strong Arthurian and Celtic associations. However most accounts have Mark, King of Cornwall ruling there during Arthur's reign.  
• Camelon/Camelot, Scotland, near Falkirk is one of the locations associated with the battle of Camlann where Arthur and Mordred were killed. However the name may also point to a "Camelot" connection.  
• The Roman fort of Camboglanna (Crook Bank), located on Hadrian's Wall has been linked to Camelot due to its name. Archaeology revealed that parts of the Wall remained occupied well into the 5th century.  
• The Roman city of Viroconium Cornoviorum is typically associated with another legendary British ruler, Vortigern. Vortigern is typically placed two generations earlier than Arthur and as the predecessor to Arthur's father. Vortigern is also associated with legends of Merlin's childhood and teenage years. Question is if it was seat of only one of the "Kings of britain" or an entire line of them. 
• Roxburgh, currently in Scotland, has been a candidate for different reasons.  Located at the center of an agricultural fertile area and center for transporting goods via river, Roxburg was heavily contested between England and Scotland for much of the Middle Ages.Several depictions of Camelot have it located near a river and the prosperity of the region may have suggested the affluent court of legend. 
• Minor candidates suggested by later scholars include Cadbury Camp , Camelford , Camelon Fort, Camlet Moat , Campus Elleti,  Chard , Graig-Llwyn  and Saltwell Park. Most for linguistic or geographical reasons.