Following the decline and fall of the Khmer empire in the 13th–15th century, the new kingdom of Ayutthaya, established in the mid-14th century in the lower Chao Phraya River or Menam area. Ayutthaya's expansion centred along the Menam while in the northern valley the Lanna Kingdom and other small Tai city-states ruled the area. Siam retained a tradition of trade with its neighbouring states, from China to India, Persia and Arab lands. Ayutthaya became one of the most vibrant trading centres in Asia. European traders arrived in the 16th century.