A steeple, in architecture, is a tall tower on a building, often topped by a spire. Steeples are very common on Christian churches and cathedrals and the use of the term generally connotes a religious structure.
Steeples generally cap bell or clock towers. Towers were not a part of Christian churches until about AD 600, when they were adapted from military watchtowers. At first they were fairly modest and entirely separate structures from churches. Over time, they were incorporated into the church building and capped with ever-more elaborate roofs until the steeple resulted. Another possiblity is that the steeple was originally a pagan structure adopted by the early Catholic church and then borrowed by the other denominations. Its purpose may have been to tell time and could have had phallic properties.
Towers are a common element of religious architecture worldwide and are generally viewed as attempts to reach skyward toward the gods. Some wooden steeples like the one in Kingston, New York pictured below are built with large wooden structural members arranged like tent poles and braced diagonally inside both with wood and steel. the steeple is then clad with wooden boards and finished with slate tiles nailed to the boards using copper over gaps on corners where the slate would not cover.