Geocentric model and planets were holes in invisible wheels surrounding Earth; through the holes, humans could see concealed fire. About the same time, Pythagoras thought that the Earth was a sphere (in accordance with observations of eclipses), but not at the center; they believed that it was in motion around an unseen fire. Later these views were combined, so most educated Greeks from the 4th century BC on thought that the Earth was a sphere at the center of the universe. In the 4th century BC, two influential Greek philosophers, Plato and his student Aristotle, wrote works based on the geocentric model.
National Register of Historic Places listings in Central Baltimore city park system are included in the federally designated Baltimore National Heritage Area. National Register of Historic Places listings in Central Baltimore This is a list of National Register of Historic Places properties and districts in downtown Baltimore, Maryland, United States. Many other properties are located in other parts of the city; for these, see National Register of Historic Places listings in Baltimore, Maryland. The locations of the National Register properties and districts listed below (at least for all showing latitude and longitude coordinates below) may be seen in a map by clicking on "Map of all coordinates". Much of