The computer colored photo shows ‘cham loh’. It was an obstacle to halt or slow down passersby. Anyone that came to face ‘cham loh’ had to change their direction to either left or right.
Once bad guys ran toward it, they had to slow down before getting torn whether they should change their direction to left or right and that gave a chance for the law officers to catch up.
In the ancient days, ‘cham loh’ were very popular. They were built around the Grand Palace of Ayutthaya Kingdom and independent lands around such as here shown in the photo which was taken at Wat Pra-Singh, the Kingdom of Chiengmai, in the reign of King Rama V.
Anyway, there is no evidence of any 'cham loh' built in the Rattakosin Kingdom.