Chatusadom

For about four hundred years, it had served as the constitution of central government of Siam or Thailand until King Chulalongkorn organized Chatusadom into modern ministries and officially established the Cabinet on April 1, 1892.

[3] Chatusadom was led by two Prime Ministers, alternatively Grand Chancellors (Thai: อัครมหาเสนาบดี) who held the rank of Chaophraya.

The chancellor of the executives in Early Ayutthaya was called Senabodi (Thai: เสนาบดี from Sanskrit Senapati) who oversaw the Ministries.

King Trailokanat organized and institutionalized the Four Ministries into bureaucratic apparatus in the Palatine Law of 1454.

The executives was led by two prime ministers; the Samuhanayok and the Samuhakalahom, who performed administrative duties on behalf of the king in Civil and Military Affairs, respectively.

King Ramathibodi II established the Krom Phra Suratsawadi (Thai: กรมพระสุรัสวดี) or the Registration Department in 1518 to specifically oversee the census of manpower for more efficient levy and conscription.

The position of Samuhakalahom had grown powerful by the mid-Ayutthaya period as he controlled military forces.

The power imbalance and potential threat from some ministers led the kings to reconsider and amend the Chatusadom bureaucracy.

Some kings preferred not to appoint Samuhanayok or Samuhakalahom to avoid creating powerful nobles, most notably King Narai, who instead assigned the duties and responsibilities of the two prime ministers to his ministers without officially investing them with titles and honors.

King Rama I restored the Southern Siamese cities to the authority of Samuha Kalahom in 1782.

The reforms culminated in 1892 when King Chulalongkorn announced the official establishment of modern Cabinet comprising twelve ministries on April 1, 1892.