The caste system of the Indian subcontinent is ruffly based on the varna system and the jati system. Although people of India share much common culture, they definitely are a very diverse nation.
The varna system consists of primarily four classes or orders which are the Brahmins, Kshatriyas, Vaishyas and Shudras. This kind of system is heavy concentrated in the Northern part of India and some of the Southern parts also.
The jati system is a system where people are divided into clans or tribes. This system is very much present in the whole Indian subcontinent.
There exists many such jatis in Sri Lanka, with many of them tracing their roots to India or at least claiming their roots from somewhere in India.
In pre-colonial times, the jatis of Sri Lanka were of great importance. There weren't "high caste" or "low caste" in the pre-colonial times. When the Europeans began colonizing the island, they used the "divide and rule" method. By giving some jatis more importance, and downplaying others. This made their job easier, because it is easier to rule them as divided then united.
There are some castes who have a more detailed accounted history then others, and thus some may have more information then the others.
The Tamil castes
In the colonial times, the Dutch registered about 40 Sri Lankan castes, but today the numbers have decreased due to assimilation. About half of the Sri Lankan Tamil population are of the Vellalar caste. The Vellalar were traditionally Farmers, Chieftains and Landlords. The word Vellalar stems from vellam (Tm. flood) and aalar (Tm. ruler), thus translated as Ruler of flood refering to agriculture. They were in pre-colonial times about 8%. They and the Govigama were one of the earliest to cooperate with the Dutch, and thus they were high ranked and were referred as Bellalas (from Tamil Vellalar).
Under the Dutch rule were there often conflicts between the Vellalar and the Madapalli. The Dutch registered the Madapalli under the Vellalar name and promoted them to intercaste marry with the Vellalar. Today the Madapalli as a community is extinct since they have completely assimilated with the Vellalar. The Vellalar enjoyed high positions under Dutch rule and thus more and more castes claimed Vellalar status, and assimilated into the bigger Vellalar society. That is why the Vellalar who were 8% now almost constitute 50% of the Sri Lankan Tamil population.
The original Vellalar are known as Saiva Vellalar, because they follow Shaiva Siddhanta. Some of them claim to have been an aristrocatic class who were important under the rule of Tamil kings in Tamilakam (historical region greater than Tamil Nadu). They have today assimilated into bigger Vellalar society. The Vellalars of today have different origins and few have this lineage in Sri Lanka. The Yalpana Vaipava Malai (The Garland of Events in Jaffna) a book written in the 1736 under Portuguese rule. It mentions often Vellalar chiefs who were of great importance in the society.
As mentioned earlier, under Dutch rule did the Vellalar have high position. They eventually introduced under Dutch rule the Thesavalamai law. This law allowed the Vellalar chiefs to have workers under them. These workers are known as Panchamars (the fives) and constituted of five castes which are the Nalavar, Paraiyar, Pallar, Ambattar and Vannar. They were servants of the Vellalars and treated as untouchables. The Nalavar were traditionally toddy tappers and are only found in Sri Lanka. The Pallar were agriculture labours. The Paraiyar's traditinaly were drummers (T. parai -drum). The Ambattar were barbers and the Vannar were responsible of washing clothes. Due to their high positions under colonial period and the Panchamars, were the the Vellalar considered to be a "high caste". They also enjoyed high government posts under post-colonial era. Arumuga Navalar and the Ponnambalam families were responsible for the high status of Vellalar and encouraged caste system to be part of the Sri Lankan institution to allowing them selves to keep their high positions.
Although the Vellalar contributed a lot to the Sri Lankan Tamil society, there were many castes who were independent of Vellalar domination. Another caste who gave great influence on the Sri Lankan Tamil society were the Karaiyar. The Karaiyar are also known as Kurukulam. The word Karaiyar is derived from the word karai (Tm. coast), thus Karaiyar is translated as coastmen. The word Kurukulam is derived from the word Kuru and kulam (Tm. clan), thus translated as Kuru clan. According to their own folklore, they were descendant of the Kurus who are mentioned in the Mahabharatha. Traditionally the Karaiyars were fishermen, chieftains and seamanship.
Although a more detailed account of them is present in the the palm leaf manuscript Mukkara Hatana (Sinh. Mukkuvar war) which was preserved by the Karavas. The Karavas were originally Tamils who assimilated into Sinhalese culture and language, and thus the Karavas and Karaiyar share common origins. According to the Mukkara Hatana the Karaiyars or Karavas, were from a place called Kurumandalam, which is the Coromandel coast of Southern India. The Karaiyar soldiers and chieftains were invited by Parakramabahu IV of Kotte to fight with the Mukkuvar. After a three month fight, the Karaiyar won over the Mukkuvar, and there were many loss in both sides. Eventually Kurukula Manikka Thalaivan, an important chieftain died, and thus Parakrambahu IV adopted his son Sapumal Kumaraya. Sapumal Kumaraya was later crowned as king under the name Bhuvanaikabahu VI. This is probably the only surviving accounts on the origins of the Karaiyars, although maybe not all trace back to Kurumandalam. The Karaiyars who stayed under Kotte rule assimilated into Sinhalese society, and the Karaiyars in Northern and Eastern part of the island remained as Tamils.
The Bharatars or Paravar, are also traditionally a fishing caste who also were involved in trade. The Mukkara Hatana along with the Karaiyar chieftains, mentions chieftains with Bharathakula before their names indicating them to be of Bharathar clan. They probably share common origin with the Karaiyars and Karavas, but maybe later gained separate identities. The Cankili II is also known to have killed 600 Paravars for converting to Christianity. They today speak both Tamil and Sinhalese and many of them have intermingled with Sinhaleses, and are listed as a separate ethnic group, and thus it seems like they are neither considered as Tamils or Sinhalese.
The Mukkuvar are traditionally fishermen and also chieftains. We know trough the Mukkara Hatana that there were Mukkuvar chieftains and soldiers also. They contributed a lot in the society of Eastern Sri Lanka, and are one of the main components of the Eastern SL Tamils. They are mention variously times in the Mattakalappu Manmiyam, a book about the history of Batticola, an important city in Eastern Province. The book which was written from collections of palm leaf scripts, mentions a conflicts between the Mukkuvar and Thimilar.
The Thimilar were concentrated in Eastern part before they lost to the Mukkuvars and Pathans (Tamil Muslims). They later migrated upwards to Northern part were they today are primarily concentrated. The word Thimilar is derived from the word thimil (Tm. boat), thus translated as boatmen. Their traditional occupation is fishing and deep sea fishing, and included chieftains. They are an really old community and are mentioned in the Akananuru of the Sangam period. The Thimilars are only found in Sri Lanka. The Karaiyars, Mukkuvars and Thimilars make up important castes involved in fishing.
There are various mentions of Brahmins in literatures of Sri Lanka. Today are they were few in number and are not drawn much attention to. A similar caste are the Kovis. Their traditional occupation was farming, but they were also temple workers. There are speculations that they were Govigamas, Sinhalese caste, who assimilated into Tamil language and culture, because of the name. But it is more likely that their name is derived from kovil (Tm. Temple).