The Great Wall is a massive L-shaped structure that bounds the pu'uhonua on its eastern and southern sides. The wall stands nearly 12 feet tall, 18 feet in width, and stretches 965 feet in length. Constructed over 400 years ago, the Great Wall continues to protect the pu'uhonua, the people, and ceremonial sites contained within from the outside world.
The Great Wall was built using traditional, dry masonry techniques in which unmodified cobbles and boulders were fitted together without the use of mortar. The structure was originally constructed with two outer walls faced with 'alā (volcanic stones, often water worn and with smooth faces). Archaeological investigations conducted in the 1919 and 1963 revealed two distinct techniques of masonry design within the interior of the structure. The first style, known as pa'o (caverned), is an open work construction technique accomplished by laying lava slabs on top of upright columns. This architectural style is unique to the park lands and, thus far, has been documented nowhere else on the Hawaiian Archipelago. The other type of interior construction noted within the Great Wall is haka haka or vacant spaces. Commonly used throughout Hawai'i Island, haka haka uses broken, angular stone rubble to fill the interior cavity of the outer walls.
Given the sheer size of the Great Wall, it remains a prominent feature on the park's landscape and therefore was the subject of numerous historical testimonies regarding the pu'uhonua. One of the earliest and well-known accounts was given by Reverend William Ellis in 1823. Ellis, both a missionary and ethnographer, noted the following:
Adjoining the Hare o Keave to the southward, we found a Pahu tabu (sacred enclosure) of considerable extent…This had several wide entrances, some on the side next the sea, the others facing the mountains…The form of it was an irregular parallelogram, walled up on one side and at both ends, the other being formed by the sea-beach, except on the north-west end, where there was a low fence. On measuring it, we found it to be 715 feet in length, and 404 feet wide. The walls were twelve feet high and fifteen thick.