Tamilakam

Tamilakam (Tamil: "tamiḻakam") refers to the geographical region inhabited by the ancient Tamil people. Tamilakam covered today's Tamil Nadu, Kerala, Puducherry, Lakshadweep and southern parts of Andhra Pradesh and Karnataka. Traditional accounts and "Tolkāppiyam" referred these territories as a single cultural area, where Tamil was the natural language and culture of all people. The ancient Tamil country was divided into kingdoms. The best known among them were the Cheras, Cholas, Pandyans and Pallavas. During the Sangam period, Tamil culture began to spread outside Tamilakam. 
Etymology.
"Tamiḻakam" is a portmanteau of a word and suffix from the Tamil language, namely "Tamiḻ" and -akam. It can be roughly translated as the "homeland of the Tamils". According to Kamil Zvelebil, the term seems to be the most ancient term used to designate Tamil territory in the Indian subcontinent.
The "Periplus of the Erythraean Sea", as well as Ptolemy's writings, mention the term "Limyrike" which corresponds to the Malabar Coast of south-western India. Based on a misinterpretation of the Roman map "Tabula Peutingeriana" and the possible phonetic connection between the words "Damir-" and "Tamil", some modern scholars have wrongly mentioned Limyrike as "Damirica" (or "Damirice"), considering it as a synonym of "Tamilakam". The "Damirice" mentioned in the "Tabula Peutingeriana" actually refers to an area between the Himalayas and the Ganges.
Extent.
The term "Tamilakam" appears to be the most ancient term used for designating the Tamil territory. The earliest sources to mention it include "Purananuru" 168.18 and "Patiṟṟuppattu Patikam" 2.5. The Specific Preface ("cirappuppayiram") of the more ancient text "Tolkāppiyam" mentions the terms "tamil-kuru nal-lulakam" ("the beautiful world [where] Tamil is spoken") and "centamil ... nilam" ("the territory ... of refined Tamil"). However, this preface, which is of uncertain date, is definitely a later addition to the original "Tolkāppiyam". According to the "Tolkāppiyam" preface, "the virtuous land in which Tamil is spoken as the mother tongue lies between the northern Venkata hill and the southern Kumari."
The "Silappadikaram" (c. 2nd century CE) defines the Tamilakam as follows:
While these ancient texts do not clearly define the eastern and western boundaries of the Tamilakam, scholars assume that these boundaries were the seas, which may explain their omission from the ancient definition. The ancient Tamilakam thus included the present-day Kerala. However, it excluded the present-day Tamil-inhabited territory in the North-East of Sri Lanka.
Subdivisions.
Kingdoms.
Approximately during the period between 600 BCE to 300 CE, Tamiḻakam was ruled by the three Tamil dynasties: the Chola dynasty, the Pandyan dynasty and the Chera dynasty. There were also a few independent chieftains, the Velirs (Satyaputra). The earliest datable references to the Tamil kingdoms are in inscriptions from the 3rd century BCE during the time of the Maurya Empire.
The Pandyan dynasty ruled parts of South India until the late 17th century. The heartland of the Pandyas was the fertile valley of the Vaigai River. They initially ruled their country from Korkai, a seaport on the southernmost tip of the Indian Peninsula, and in later times moved to Madurai. The Chola dynasty ruled from before the Sangam period (~3rd century BCE) until the 13th century in central Tamil Nadu. The heartland of the Cholas was the fertile valley of the Kaveri. The Chera dynasty ruled from before the Sangam period (~3rd century) until the 12th century over an area corresponding to modern-day western Tamil Nadu and Kerala.
The Vealirs ("Vēḷir") were minor dynastic kings and aristocratic chieftains in Tamiḻakam in the early historic period of South India.
Nadus of Tamilakam.
Tamiḻakam was divided into political regions called "Perunadu" or "Great country", "nadu" means country.
There were three important political regions which were Chera Nadu, Chola Nadu and Pandya Nadu. Along these three there were two more political regions of Athiyaman Nadu (Sathyaputha) and Thamirabharani Nadu (Then Paandi) which were later on absorbed into Chera resp. Pandya Nadu by 3rd century BCE. Tondai Nadu which was under Chola Nadu, later emerged as independent Pallava Nadu by 6th century CE.
Again Tamilakam were divided into 12 socio-geographical regions called "Nadu" or "country". Each of this Nadu had their own dialect of Tamil.
Nadus outside Tamilakam.
Some other "Nadus" are also mentioned in Tamil literature which were not part of Tamilakam, but the countries traded with them in ancient times.
Tamil speaking lands:
Other:
Geocultural unity.
Although the area covered by the term "Tamilakam" was divided among multiple kingdoms, its occurrence in the ancient literature implies that the region's inhabitants shared a cultural or ethnic identity, or at least regarded themselves as distinct from their neighbours. The ancient Tamil inscriptions, ranging from 5th century BCE to 3rd century CE, are also considered as linguistic evidence for distinguishing Tamilakam from the rest of South India. The ancient non-Tamil inscriptions, such as those of the northern kings Ashoka and Kharavela, also allude to the distinct identity of the region. For example, Ashoka's inscriptions refer to the independent states lying beyond the southern boundary of his kingdom, and Kharavdela's Hathigumpha inscription refers to the destruction of a "confederacy of Tamil powers".
Cultural influence.
With the advent of the early historical period in South India and the ascent of the three Tamil kingdoms in South India in the 6th century BCE, Tamil culture began to spread outside Tamiḻakam. Prior to 3rd century BCE, more Tamil settlers arrived in Sri Lanka. The Annaicoddai seal, dated to the 3rd century BCE, contains a bilingual inscription in Tamil-Brahmi.Though Tamils have been living in Sri Lanka since the Ancient era at least the past in a more inclusive way:Interview with Dr. Sudharshan Seneviratne|journal=Frontline|date=27 January 2006|volume=23|issue=1|url=http://www.hindu.com/thehindu/thscrip/print.pl?file=20060127003610200.htm&date=fl2301/&prd=fline&|access-date=9 July 2008}}</ref> Excavations in the area of Tissamaharama in southern Sri Lanka have unearthed locally issued coins produced between the second century BCE and the second century CE, some of which carry local Tamil personal names written in early Tamil letters, which suggest that local Tamil merchants were present and actively involved in trade along the southern coast of Sri Lanka by the late classical period. Around 237 BCE, "two adventurers from southern India" established the first Tamil rule at Sri Lanka. In 145 BCE Elara, a Chola general or prince known as Ellāḷaṉ took over the throne at Anuradhapura and ruled for forty-four years. Dutugamunu, a Sinhalese, started a war against him, defeated him, and took over the throne. Tamil Kings have been dated in Sri Lanka to at least the 3rd century BCE.
Religion.
Hindus, Jains and Buddhists have coexisted in Tamil country for at least as early as the second century BCE.