A sima is a boundary stone, and in the north-east of Thailand, in the region called Isan, hundreds of them stand in fields and temple grounds, many of them more than a thousand years old. Monks placed them in rings around ordination halls, to mark the sacred space where the Buddhist community could meet, and in the Dvaravati period, between roughly the seventh and eleventh centuries, carvers began to decorate them with scenes from the life of the Buddha. The sima at the site in this listing are part of a UNESCO inscription that recognises this tradition, found nowhere else in such density.
The stones are often slabs of the local sandstone, standing upright and weathered by rain, with reliefs showing the Buddha's birth, his teaching and scenes from his earlier lives, drawn in a simple, vigorous style. Sometimes they are placed in the shelter of rock formations, among boulders, and sometimes in an open temple compound under tall trees. The whole region is dotted with sandstone outcrops and rock shelters, some with prehistoric paintings, which made it a place of religious significance long before the Dvaravati period.
The ride from Vientiane begins across the Mekong by the Friendship Bridge, which Thai and Lao authorities have operated since 1994, with border formalities to deal with on both sides, then continues through Nong Khai and south along the highway to Udon Thani. The road is straight, flat and fast, with long views of rice fields, sugar cane and cassava, and the main hazard is slow trucks. Thailand drives on the left, so riders from Laos have to switch sides at the crossing. The best months are November to February, when it is cool and dry. From April to October, heat and heavy rain make it harder.
Nam Som, the nearest sizeable town, has about nineteen thousand people and is a good place to buy fuel, food and water. Thai roadside restaurants are excellent: look for grilled chicken, papaya salad, sticky rice and sweet iced tea, the staples of Isan cooking. Bring cash, and remember to take off your shoes before entering temple buildings. Go early, since the sun is hot, and the stones are best seen in low light.