A fort is a large open area enclosed by a wall and designed to house many troops.

The Romans had many forts scattered around the countries where they had an empire.

A castle is not the same as a fort. A castle is a private home while a fort is a place for troops.

The largest number of forts are in the United States. There are forts dotted about over almost all states. This is because forts were used by fur traders in the early days of the frontier, and also by surveyors. Later on, as large numbers of pioneers moved west across the Great Plains, so the government set up military forts to help to control the environment where Native Americans, railroad and pioneers were all in conflict. All of these were simple wooden walled forts because they were never meant to last very long. Fort Steuben, in the video below, is a typical early frontier fort.