Manthai (Tamil: மாந்தை, romanized: Māntai) is a coastal town and an ancient harbor situated in the Mannar district, of the Northern Province of Sri Lanka.

[8] With the likes of Arikamedu and Karaikadu of Tamil Nadu, Manthai was a major exporter of beads since the early first millennium AD.

According to Dr. Paul E. Peiris, an erudite scholar and historian, Thiruketheeswaram in Manthai was one of the five recognized Eeswarams of Siva in Lanka very long before the arrival of Vijaya in 600 B.C [11] During the reign of the Cholas, between the 10th and 11th Centuries C.E., the town had developed into a major port, with many highways and served as an important link between the island and the mainland Chola kingdom.

[13] Mathoddam is currently viewed as the only port on the island that could be called a "buried city," with much of the ancient ruins under sand today.

Manthoddam finds mention as "one of the greatest ports" on the seaboard between the island and Tamilakam in the Tamil Sangam literature of the classical period (600 BCE - 300 CE).

The shrine's initial installment is credited to the indigenous Karaiyar Naga tribe, The Karaiyars claimed to be related to several classical period public figures hailing from the international port town, including the creator of the oldest extant Tamil literature by a Sri Lankan Tamil, the Sangam poet Eelattu Poothanthevanar.

The local Tamils under the urging of the famous Hindu reformer Arumuka Navalar rebuilt the present-day temple at its original site.

An effigy of Lord Ketheeswarar is immersed in the scared tank as a part of the ritual bath, during the annual temple festival.

Manthai, known as Mahathiththa during ancient times, was situated north of the mouth of the Malvathu River (Aruvi Aru).