Ancient Indian seaport/harbor-town mentioned in the Graeco-Roman writings
Tyndis (, Tamil: Thondi) was an ancient south Indian seaport/harbor-town mentioned in the Graeco-Roman writings. It was located north of port Muziris (Muchiri) — by around 500 stadia — in the country of the Chera rulers. No archaeological evidence has been found for Tyndis.
Chera rulers of early historic south India (c. second century BCE - c. third century CE) had their headquarters at Karur (Karuvur) in the interior Tamil Nadu and harbors at Muziris (Muchiri) and Tyndis (Thondi) on the Malabar Coast (present-day Kerala). There are several references to a port with the name Thondi, on the Kerala coast, in the Chera country, in early historic Tamil texts. 
Thondi, a town with same name in the Pandya country, on the eastern coast of the peninsula, is also mentioned in early Tamil literature. This town still exists with the same name.
Different variations of the name.
The term "Thondi" in Tamil refers to either "a small bay-like landscape" or the "navel". Thondi, like Virai or Arikamedu-Virampattinam, is sometimes referred to as "Munthurai" or "the port in front [of the town] in the sources. It is also called "Kanalam Thondi" or "the coastal town with backwater lakes" or backwaters with flowers. It is also described as "valam kezhu", signifying its riches, much like Muziris (Muchiri), in the Tamil poems.
The Thondi port also had a goddess ("Ananku").
Sources.
Early Tamil texts.
There are several references to a port with the name Thondi, on the Kerala coast, in the early Tamil texts. It was under the control of the Chera rulers (probably under the Irumporai collateral branch). It was perhaps associated with the hinterland trade from the Malabar Coast to interior Tamil country via the Palghat Gap. 
The Chera ruler of Thondi was usually called "Poraiyan". One ruler, notably called "Thin Ther Poraiyan" or "the Poraiyan Chera with the Strong Chariot", finds repeated mention in the early Tamil literature. In some occasions, Chera ruler of Thondi is directly named as "Chenkol Kuttuvan" or Cheraman Ko Kothai Marpan. 
There are mentions of a "palace" of the Chera ruler in Thondi. The Chera ruler, according to early Tamil poems, fixed the tooth of his enemy chieftain "muvan" on the gate of this palace. Ruler of Thondi seems to have had a contingent of Marava people among his fighters and was in possession of several elephants. He also handed out coins to bards or poets and, in once instance, gifted varudai (mountain) goats from the Deccan region (?) to the Brahmin priests.
There are mention of extensive rice or paddy cultivation in the fields in and around Thondi ("the coastal town with backwater lakes" or backwaters with flowers). Early Tamil poems also hint at coconut trees, and some hills "around" Thondi.
Thondi was also famous for its fishing and "neythal" flowers. It also had a fishing community of Paratavar people.
Location.
The location of Muziris provides clues for the location Tyndis, which was 500 stadia (92 km) north of it ("by river and sea"). The exact location of the port is still unknown. 
Possible candidates include the following modern locations:
References.
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