This elaborately planned site may have been the northernmost outpost of Cahokia, although it is also now known that some Siouan peoples along the Mississippi River may have taken part in the culture as well. Regardless, the Mississippian site traded with and was clearly influenced in its civic and defensive planning, as well as culturally, by its much larger southern neighbor. A rectangular wood-and-clay stockade surrounded the twenty acre site, which contained two large earthen mounds and a central plaza. One mound may have been used for food storage, as a residence for high-ranking officials, or as a temple, and the other may have been used as a mortuary. The Mississippian culture cultivated maize intensively, and their fields probably stretched far beyond the stockade at Aztalan, although modern agriculture has erased any traces of Mississippian practices in the area. Some rumors also speculate that the people of Aztalan may have experimented slightly with stone architecture in the making of a man-made, stone-line pond, at the very least. While the first settler on the land of what is now the city supposedly reported this, he filled it in and it has yet to be rediscovered. Both Woodland and Mississippian peoples inhabited Aztalan, which was connected to the extensive Mississippian trade network. Shells from the Gulf of Mexico, copper from Lake Superior and Mill Creek chert have been found at the site. Aztalan was abandoned around 1200 AD. The Oneota people later built agriculturally based villages, similar to those of the Mississippians but without the extensive trade networks, in the state. By the time the first Europeans arrived in Wisconsin, the Oneota had disappeared. The historically documented inhabitants, as of the first European incursions, were the Siouan speaking Dakota Oyate to the northwest, the Chiwere speaking Ho-Chunk (Winnebago) and the Algonquian Menominee to the northeast, with their lands beginning approximately north of Green Bay. The Chiwere lands were south of Green Bay and followed rivers to the southwest. Over time, other tribes moved to Wisconsin, including the Ojibwe, the Illinois, the Fauk, the Sauk and the Mahican. The Mahican were one of the last groups to arrived, coming from New York after the U.S. congress passed the Indian Removal Act of 1830. Exploration and colonization French period The first European known to have landed in Wisconsin was Jean Nicolet. In 1634, Samuel de Champlain, governor of New France, sent Nicolet to contact