Formerly, Krungthep Mahanakhon was called "Muang Bang Kok." When King Rama the Great performed the ceremony of the City’s pillars sanctuary on April 21, 1782, he changed its name to "Krungthep Rattanakosininth Ayothaya." During the reign of King Rama III, the name of the city was transformed into "Krungthepmahanakhon Bawonrattanakosin Mahintha Ayutthaya." In the following reign, King Rama IV modified this name by changing the word "Bawon" to "Amon," "Mahintha Ayutthaya" to "Mahinthra Yutthaya" and adding some suffix.
This capital city has the longest name in the world: “Krungthep Mahanakhon Amon Rattanakosin Mahinthra Yutthaya Maha Dilok Phop Noppharat Ratchathani Burirom Udom Ratchaniwet Mahasathan Amonphiman Awatansathit Sakkathatthiya Witsanukamprasit.”
Thai language:
กรุงเทพมหานคร อมรรัตรโกสินทร์ มหินทรายุธยา
มหาดิลกภพ นพรัตนราชธานีบูรีรมย์
อุดมราชนิเวศน์มหาสถาน อมรพิมานอวตารสถิต สักกะทัตติยวิษณุกรรมประสิทธิ์
Romanization:
Krungthep mahanakhon Amon rattanakosin Mahinthra yutthaya
Maha dilok phop Noppharat ratchathani burirom
Udom ratchaniwet mahasathan Amonphiman awatansathit Sakkathatthiya witsanukamprasit
Translation:
City of angels, great city of immortals
Magnificent city of the nine gems, throne of the King
City of Royal Palaces, residence of Gods incarnate Erected by Visvakarman at Indra’s Behest
Edited and translated in three languages by SUKO Translation
Source
The Royal Institute of Thailand (http://www.royin.go.th/?knowledges=กรุงเทพมหานคร)
Centre d’information de Bangkok (http://203.155.220.230/m.info/bangkokforyou/bangkokforyou.html)