Soldiers' Home Reef in Milwaukee is a fossilized coral reef formed about 400 million years ago during the Silurian period, when this part of Wisconsin lay beneath a shallow tropical sea. Preserved in limestone are corals and marine animals such as trilobites, cephalopods, brachiopods, bryozoans, bivalves, and pelmatozoans. Glaciation later reshaped but did not destroy the hard mound, and erosion by the Menomonee River re-exposed it. In the 19th century, fossils collected here helped Increase A. Lapham and James Hall recognize these outcrops as ancient reef structures, leading to the first identification of fossilized reefs in North America. Its survival also aided later geological research and helped make it nationally significant.