used to mark the site for travelers, but this is not certain. They may also have been used for announcements, message relays, or for calculations of astronomical phenomena, as has been found at other Mississippian sites, such as Cahokia. Stockade The settlement was surrounded on the north, west, and south sides by a palisade, a wall of logs set vertically into the ground. Narrow holes were dug into the ground, then the posts were lifted into position and set into the holes. The stockade was finished by people weaving flexible willow branches through the posts, and plastering the whole with a mixture of clay and grass to fill in the gaps, a technique similar to wattle and daub. At some point, a smaller stockade was built within the outer one to delimit the dwelling areas. Archeologists have not been able to determine whether both stockades existed simultaneously, for a layered defense, or one was built after the other fell into disuse. In 1850, Increase A. Lapham, an author, scientist, and naturalist, surveyed the site on behalf of the Smithsonian Institution, which was surveying ancient mounds. He described the outer stockade as being " long at the north end, long on the west side and on the south side; making a total length of wall of . The ridge or wall is about , and from to ) in height". It had at least 33 square bastions at regular intervals along its length, similar in form and placement to some European fortifications, to allow defensive warriors to cover that area by shooting arrows. In addition, others were built along the secondary walls. Rather than having a gate to protect the entrance, the builders constructed the entrance so that it was camouflaged from direct view and blended in with the wall on either side. During the time Aztalan was inhabited, two sets of outer stockades were built. The posts of the first one eventually rotted, and the second one burned and was never rebuilt. It is not clear whether the purpose of the stockade was to keep out invaders, or if the occupants built it for another reason. Modern discovery (1835–1919) A young man named Timothy Johnson discovered the ruins of the ancient settlement in December 1835. In January 1836, N. F. Hyer conducted the first rough survey of the site, and published his discovery in the Milwaukie Advertiser of January 1837.