Final answer:
A trilithon consists of two large vertical stones supporting a third horizontal stone, a construction technique called post-and-lintel, which is notably used in Stonehenge.
Step-by-step explanation:
The term trilithon refers to an architectural structure consisting of two large vertical stones (posts) supporting a third stone set horizontally across the top (lintel). This design is most famously observed at Stonehenge, where several trilithons are arranged in a circular formation. The construction technique associated with trilithons, known as post-and-lintel, was a significant architectural advancement in Neolithic times. Trilithons and post-and-lintel constructions can be found in various ancient structures and have also been incorporated into the design of underground burial chambers like passage graves. Notably, the creation and transportation of these megalithic structures, such as the bluestones and Sarcen stones used in Stonehenge, required sophisticated methods involving felled trees and earthen mounds, with the additional use of key stones in certain types of arches.