The number of towers on any structure is the quantity of visually distinct towers or turrets rising from the base of the structure up to a point higher than its roofline. Although a tower should usually appear as a distinct element over its entire height, it should be counted as long as it rises high over the roofline and forms a dominant part of the structure's form. Also, if a tower does not rise more than a slight amount over the main roofline, but nevertheless has the distinct appearance of a tower all the way up the height of the structure, then it should be counted.

Common types of towers counted in this field are steeples, minarets, bell towers, and fortification towers.

Spires, finials, fleches, lanterns, turrets, and other small or medium-sized decorative towers which start at the roof, setback, or cornice level, should not be counted as towers.

Freestanding towers (such as bell towers or minarets), which are not attached to the building being described, should not be counted as towers for that building.

This field may apply to many types of building, but is especially common in religious structures (e.g. churches and mosques) as well as castles.