Why did the Siamese kingdom of that era need two capitals? Besides Ayutthaya, why was Lopburi also chosen? The answer lies with King Narai the Great, who observed that Ayutthaya's location was vulnerable to sieges and cannon attacks from enemies. To safeguard the kingdom, he established a second capital in Lopburi. French and Italian engineers were commissioned to design and construct a palace, fortifications, and city walls, resulting in what is now known as Narai Palace or Phra Narai Ratchaniwet.

Located in Mueang District, Lopburi Province, Phra Narai Ratchaniwet was constructed in 1666 on a 41-rai (approximately 16-acre) plot to serve as the king's residence, a place for royal duties, and a venue for hosting foreign dignitaries. After King Narai's death, the palace fell into disuse until King Mongkut (Rama IV) restored it in 1856. He used it as a residence and inner capital, renaming it "Phra Narai Ratchaniwet." Today, parts of the palace complex house the Somdet Phra Narai National Museum, though locals often refer to it simply as "Narai Palace."

The palace grounds are divided into three sections: the outer, middle, and inner courts. During King Narai's reign, many significant buildings were constructed, such as the Chanthara Phisan Pavilion, Dusit Sawan Thanya Maha Prasat Hall, and the Phiman Mongkut Pavilion group.

Over time, many structures from King Narai's era deteriorated, with most losing their roofs and retaining only walls and floors. However, their architectural styles remain distinct. Some buildings, especially those restored during King Mongkut's reign, are still in excellent condition and in use today. For instance, on October 11, 1924, Prince Damrong Rajanubhab and Prince Narisara Nuwattiwong established a museum in the Chanthara Phisan Pavilion, initially named "Lopburi Museum." In 1961, it was renamed "Somdet Phra Narai National Museum," which has since expanded its exhibits to include the Phiman Mongkut Pavilion.