The bell towers are perhaps the most beautiful and remarkable features of the missions in California. The bells were rung at mealtimes, to call residents to work and worship, during special events such as births and funerals, to signal the approach of a ship, or to sound an alarm.

In the Spanish mission system of the 18th and 19th centuries, the bell tower (or "campanario") was the most vital architectural and functional element of the settlement, serving as the mission's primary means of communication. Since the indigenous populations and the Spanish friars did not use clocks, the bells dictated every second of daily life. The tower was designed to be the tallest structure so that the sound of the bells could travel for several miles across the surrounding agricultural fields and ranch lands. Specific bell rhythms and "tolls" signaled the start of morning prayer, the beginning and end of work, meal times, and bedtime. Beyond daily routine, the bell tower was a "social broadcaster": joyful peals announced weddings or the arrival of dignitaries, while slow tolling signaled a death or a funeral. Importantly, the tower also served as a security alarm; a frantic, rapid ringing warned of an impending attack or a fire, allowing everyone to flee to the safety of the mission's thick adobe walls. Symbolically, the bell tower was also meant to represent the presence of the Church and the Spanish Empire in a "new" territory, serving as a landmark for travelers and a sign of a settled, organized community in what the Spanish perceived as a vast and un-ordered wilderness.