Wat Phra Chao Phya-thai. populary known as Wat Yai Chaimongkol, is situated to the southeast of the city. The large chedi there can be seen from a great distance. It was built by King U-thong in 1357 A.D.
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In 1592 A.D. during the reign of King Naresuan the Great, the Burmese led an army to try to subjugate Ayutthaya. King Naresuan resisted the invasion and fought on elephant back with the Burmese leader at the district of Nong Sarai in the province of Suphanburi, and was victorious.
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On that occasion, King Naresuan's army was not able to inflict greater losses on the Burmese because many of his regiments did not come to reinforce him in time.
The King wished to execute the officers of those regiments at the conclusion of the war, but Patriarch Vanarat begged the King to pardon them and advised him to build chedis in memory of his great victory.
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So King Naresuan built one on the scene of the singlehanded combat at Nong Sarai in Suphanburi, and a bigger one on the premises of Wat Chao Phyathai. This second chedi built by King Naresuan was named Phra Chedi Chai Mongkol, or Chedi of the Auspicious Victory, and it was popularly known as Phra Chedi Yai, or the Great Pagoda.
So. later on Chao PhyaThai came to be known also as Wat Yai Chai Mongkol. The top of this chedi is visible to visitors from Bangkok as soon as they enter the boundary of Ayutthaya.