Bai sema

Bai sema (Thai: ใบเสมา, pronounced [bāj sěː.māː]) are boundary stones which designate the sacred area for a phra ubosot (ordination hall) within a Thai Buddhist temple (wat); otherwise called sema hin (เสมาหิน).

Before work starts on a new phra ubosot, nine holes are dug: eight at the cardinal points, the ninth beneath where the principal Buddha statue will be placed.

Luk nimit (Thai: ลูกนิมิต), round stones the size of a cannonball, are placed in to these holes during a religious ceremony.

Double (or even triple) bai sema signify that the phra ubosot has been rebuilt, or consecrated for use by more than one monastic order, or that the temple has a Royal connection (photo 1).

The Thammayut order, which was founded by Prince Mongkut (the later King Rama IV) in 1833, developed a three-dimensional form of bai sema (photo 4).