The Phra Khlang was the minister responsible for external relations and maritime trading affairs. He was in charge of the royal warehouses, the commercial monopolies, and the relations with foreigners. The Phra Khlang, referred to as the "Barcalon" by Western foreigners, was, in fact, the king's personal merchant.
The collection of local products was done through the system of 'suai', royal tributes gained from the dominions. These tributary goods, as well as the incoming goods of high value and arms, were stored in the royal warehouses, ready to be exported. [3]
In the 'Geographical description of Ayutthaya: Documents from the palace', the following storehouses or treasuries were situated outside the Grand Palace. [4]
- The Inner storehouse was beside the Crystal Pond of the Grand Palace. (1)
- The Government storehouse was beside the road of Wat Na Pa Fai. (2)
- The Goods storehouse was beside the Banana Leaf Quarter.
- The warehouse storing gear for war horses was beside the wall of Wat Thammikarat.
- The Inner and Outer Customs storehouses were beside the Jao Phrom Market Road. (3)
- An Armament storehouse was situated along the Nakhon Ban Canal.
- Two other Armament storehouses were by Wat Si Chiang.
- A warehouse building to store bullets and saltpetre (for gunpowder) was in front of Wat Jan and behind Wat Sangkha Phat.
- A warehouse building to store elephant harnesses and gear is beside Wat Yanusenthon. (4)
- There might have also been a warehouse to store articles for festivities, but the text in reference [4] is unclear.