Wat Ket dedicates to the guardian spirit Jao Ket, the spirit of the Ho Klong or drum tower, which stood in its vicinity. The drum tower was a massive structure on which top officials beats the drums to warn the populace in the case of fire or other danger. This tower has since long disappeared. Jao Ket was a true spirit (phi) created by sacrificing a suitable individual as the Jao Ho Klong spirit. Then they buried the poor individual in the foundations underneath the structure (foundation sacrifices). [1]
In my opinion Engelbert Kaempfer, a medical doctor working for the Dutch VOC (Verenigde Oost-Indische Compagnie) and on a visit to Ayutthaya in 1690 CE, has Wat Ket drawn on his original sketch. The key reads “Regiu templu q. alteru aque de”, which I would translate as “Royal or magnificent temple and a watercourse on both sides.” (2)
The restored ruin of Wat Ket is in geographical coordinates: 14° 21' 9.38" N, 100° 33' 36.08" E.
Footnotes:
(1) The main road in the centre of the city, 11 metres (six fathoms) wide and paved smooth with laterite for big events such as processions and military parades, often started from the Victory Gate, south of the city. It was called Phra Khlang Street (Rue du Barcalon for the French) by the westerners. [2].
(2) Regiu (Regius) [Royal], templu (templum) [temple], q. (que) [and], alteru (alterutrique) [on both sides], Aque [watercourse] - Transcription of writing on Kaempfer sketch map in Terwiel/Sternstein 'Prospects of Ayutthaya, Capital of Siam 1690', pp.166-8.