A prang is a tall finger-like spire, usually richly carved. This was a common feature of Khmer religious architecture and was later adopted by Thai builders, typically in the Ayutthaya (1350–1767) and Bangkok periods. In Thailand it appears only with the most important religious buildings.
The first Prangs in Thailand were built e.g. in Phimai and Khao Phnom Rung and Lopburi between the early 10th century and the late 12th century, when the Khmer kingdom was dominant. They influenced the old Khmer architect, who also built great temple complexes such as Angkor Wat and Angkor Thom, remarkably resembling north Indian temples, whose Sikhara ("temple towers", also called Rekha) the Khmer prangs remarkably resemble.
Originally in the Khmer temples Hindu gods (Shiva and also Brahma) were worshipped. The areas where the holy tower was (the Cella) was relatively small, for two reasons:
The Cella was entered via a small porch, usually aligned to the east, which was called the Mandapa. Over the cubic Cella rose the central tower, the bud-shaped Prang, modeled after the cosmic mountain Meru, crowned by a top stone in form of a lotus bud.
After the Khmer realm collapsed, the Thai building masters of Sukhothai adapted the Prang form. They extended and developed it. The building material was no more separate small sandstone blocks, instead the Thais built the Prang in brick or laterite covered with stucco. And the Cella could be reached only by stairs. An example for this is the Prang of the Wat Mahathat in Phitsanulok. Later developments of the Prang suggested the Cella only. The entrance door became a niche, in which was placed the Buddha statue, which had originally taken the central position inside. For reasons of symmetry the niche was repeated on all four sides. On its pinnacle was a Trishul, the "weapon of Indra".
A "more modern" Prang is a slim construction, like an ear of corn, which lets its Khmer origin be only suspected. The best example is Wat Arun, the landmark of Bangkok. Also Wat Phra Kaeo has six thin Prangs arranged in a row. Another example is the four Prangs arranged in all four directions around Wat Pho in Bangkok, and the five Prangs in Wat Pichayart in Thonburi.