Mystery Hill is an archaeological site in the northeastern United States that contains a number of unusual stone structures, Including large upright-standing stones. There is a popular folk belief that the structures at Mystery Hill were built by ancient Europeans more than 1,000 years ago. That would mean that Europeans were present in North America much earlier than previously thought. Several features of Mystery Hill appear to support this belief.

First, the arrangement of stones at Mystery Hill is similar to that of some stone structures that are well known in Europe. For example, Stonehenge, an ancient monument in England, includes large stones that align with astronomical events, such as the position of the Sun at sunrise on the longest day of the year. Certain stones at Mystery Hill align with the same events in precisely the same way. This same arrangement at both locations suggests that the builders of Mystery Hill were inspired by European monuments.

Second, researchers discovered a large flat stone at Mystery Hill that appears to have an early type of European writing carved into it. The particular writing system, consisting of straight lines, was used by Irish people in Europe, starting about 1,500 years ago. The presence of a stone containing very old European writing at Mystery Hill suggests that Europeans were present at the site long ago.

Finally, archaeologists determined that the large stones at Mystery Hill were quarried, or cut from the ground, and then significantly altered by hammering and burning well over 1,000 years ago. The way in which stones at Mystery Hill were quarried and the methods used to reshape them are similar to quarrying activities and stoneworking methods that ware widely practiced in Europe in the distant past. Such methods are not generally associated with ancient Native Americans.