The serpent on the stairway
Almost every set of temple steps along this river is flanked by a naga, the serpent of the water. It is not decoration: the naga marks the boundary between the ordinary world and the consecrated one, and you climb along its body to cross it.
Count the heads. A single head, three, five, seven or nine: the number is a statement about the building's status and the tradition it belongs to, and it varies between Lao, Thai and Khmer practice in ways that are consistent enough to use as a guide.
The buildings are not alike and not unrelated. They are dialects of one language, and the river is what carried it.
What the hands are saying
Buddha images are not portraits, they are positions. A hand raised palm-outward is the gesture of dispelling fear; a hand hanging down to touch the earth is the moment before enlightenment, calling the ground itself as witness.
Thailand assigns images to days of the week, which is why a Thai wat often holds eight of them rather than one, and why people make offerings at the one matching the day they were born.
Roofs, and what a kingdom could afford
Lao sim roofs sweep low and layered, sometimes nearly to the ground; Thai roofs rise steeply and end in a chofa, the thin horn at the ridge. Bagan's brick stupas do something else entirely, because they were built before either tradition took its present shape and in a place with no good building stone.
Materials explain more than style does. Ayutthaya built in brick and covered it in stucco; Angkor had sandstone and laterite within reach and carved accordingly. The differences you see along the river are often a question of what was quarryable nearby.
