Ko Kaeo, or Crystal Island, is mentioned a few times in the Royal Chronicles of Ayutthaya. Ayutthaya was on three sides surrounded by the Lopburi River, but the eastern city border was its weakest point in 1568 CE, as at that time there was only a moat between the Rattanachai Gate in the north and Kaeo Island in the south. (4)
We read in the chronicles: "The officials and men of all the cities of Chainat, Suphanburi, Lopburi, Inburi, Phetburi, Ratburi, Nakhon Nayok, Saraburi, Phromburi, Sanburi, Singburi, Nakhon Chaisi, Thonburi, and Marit occupied the positions from the Ratanachai corner down to Kaeo Island the side so constituted, not being separated by the river from the land, had only a moat." [1]
The Burmese, preparing for the attack on Ayutthaya, made earthen causeways towards the Siamese front ramparts at three points. One of these points was the corner of Ko Kaeo, where the King of Ava was positioned.
"When the inventory of all the troop supplies ordered by the King was completed, the King of Hongsawadi had preparations made for attacking the Capital and ordered causeways laid extending in towards the front ramparts of the city from three points from the positions of the Uparat the first was to be laid extending in to Fang Monastery and a second to Ian Village, and from the positions of the King of Ava a third was to be laid extending in to the corner of Kæo Island. In laying the earth in towards the city the men of Hongsawadi constructed shields and set them up running in towards the city to protect themselves from firearms, and they heaved the earth on ahead over the shields." [2]
The Siamese on Crystal Island could not withstand the Burmese land attack, additionally supported on the flanks by a naval force (likely on both canals surrounding Ko Kaeo). The Siamese fled into their enclosure, and the wall on the corner of the island was penetrated and destroyed. The loss of Crystal Island would finally lead to the first fall of the City of Ayutthaya in 1569 CE.
“Meanwhile, Phraya Ram, Phra Kalahom and Phra Maha Thep seeing the army being protruding towards them, ordered the erection of one-storied, semicircular stockades on the ramparts of the Capital and brought up cannon and monthok guns to be set up in abundance in the face of the stockades. The troops at their posts on the walls and earthworks still fought on to defend the city. The King of Hongsawadi had his troops brought in along the causeway at the corner of Kæo Island, had the naval forces brought in on the flanks, and had carong, monthok, and trigger guns fired in salvos like a rainstorm at the officials in order to seize the Kæo Island corner. The picked troops stationed at the Kæo Island corner, unable to fight and defend themselves, fled down into the stockade which they had established, and the men of Hongsawadi managed to penetrate to, and destroy, the wall at the Kæo Island corner.” [3]