Wat Arun Ratchawararam Ratchawaramahawihan (Thai: วัดอรุณราชวราราม ราชวรมหาวิหาร pronunciation^ⓘ ) or Wat Arun (Thai pronunciation: [wát ʔarun], "Temple of Dawn") is a Buddhist temple (wat) in the Bangkok Yai district of Bangkok, Thailand. It is situated on Thonburi on the west bank of the Chao Phraya River. The temple derives its name from the Hindu god Aruṇa, often personified as the radiations of the rising sun. Built with a fusion of Indian, Chinese, and Khmer influences, incorporating elements of both Hindu and Buddhist symbolism, as well as reflecting Siamese tradition and identity. Wat Arun is among the best known of Thailand's landmarks. Although the temple has existed since at least the 17th century, its distinctive prang (spire) was built in the early 19th century during the reigns of Rama II and Rama III.

The name of Wat Arun is derived from the Hindu god Aruna, who is charioteer of the sun god Surya.

A Buddhist temple had existed at the site of Wat Arun since the time of the Ayutthaya Kingdom, prior to the reign of King Narai. It was then known as Wat Bang Makok which was later shortened to Wat Makok, after the village of Bang Makok in which it was built (makok is the Thai name for the Spondias pinnata plant). According to the historian Prince Damrong Rajanubhab, the temple was shown in French maps during the reign of Narai (1656–88), drew by Claude de Forbin and de Lamare.

The temple was renamed Wat Chaeng by Taksin (1767–82) when he established his new capital of Thonburi near the temple, following the fall of Ayutthaya. It is believed that Taksin vowed to restore the temple after passing it at dawn. The temple enshrined the Emerald Buddha image before it was transferred to Wat Phra Kaew on the river's eastern bank in 1785. The temple was on the grounds of the royal palace during Taksin's reign, before his successor, Rama I (1782–1809), moved the palace to the other side of the river. It was abandoned until the reign of Rama II (1809–24), who had the temple restored and had begun plans to raise the main pagoda to 70 m. The work on the pagoda commenced during the reign of Rama III (1824–51). The main prang was completed in 1851, after nine years of continued construction.

In 1858, Henri Mouhot, a French expeditioner, recorded the detailed observations of Wat Chang (literally Wat Chaeng, Wat Arun) in his travel journals Voyage dans les royaumes de Siam, de Cambodge, de Laos when he had journeyed to Siam.

Nous devons ajouter que la plus belle pagode de Bangkok, celle de Wat-Chang, n’est cependant pas renfermée dans l’enceinte du palais, mais s’élève vis-à-vis, sur la rive droite du Ménam. Sa flèche, haute de deux cents pieds, est le premier indice de la capitale qu’aperçoit le voyageur qui remonte le fleuve en venant de la mer.

(Translation): Let me add here that Wat Chaeng, the most beautiful temple in Bangkok, is not located in the palace grounds but stands majestically on the right bank of the river. The spire of the pagoda, which is over 200 feet in height, is the first sign to travelers sailing upstream from the mouth of the river that they have arrived in the capital.

— Henri MOUHOT (1826–61), Voyage dans les royaumes de Siam, de Cambodge, de Laos, 1868.