Why go
Older maps and travel accounts may call Thailand Siam, especially when discussing Ayutthaya and later Bangkok. Recognizing the name helps place those sources in time rather than treating Siam as a separate destination. The Portuguese mission to Ayutthaya after the conquest of Malacca is one concrete example of the foreign contacts through which the label circulated.
The full story
Names in Thai and foreign records followed different paths. The older word Siam became familiar in European accounts of the kingdoms in what is now Thailand, while Mueang Thai was used within Thai society. The exact origin of Siam is less useful to a traveler than the distinction between those viewpoints. When reading about Ayutthaya, foreign merchants and diplomats may describe a “Kingdom of Siam” even though the places on the map are in present-day Thailand. Portuguese contact offers a clear example: after taking Malacca in 1511, Portugal sent a diplomatic mission to Ayutthaya. Later European accounts kept the name Siam in circulation. That history is worth remembering at Ayutthaya’s ruins and in Bangkok’s older royal quarter, where several eras are often discussed under different names.