Within any parish, the local church is often the oldest building and is larger than any pre-19th-century structure except perhaps a barn. The church is often built of the most durable material available, often dressed stone or brick. The requirements of liturgy have generally demanded that the church should extend beyond a single meeting room to two main spaces, one for the congregation and one in which the priest performs the rituals of the Mass. To the two-room structure is often added aisles, a tower, chapels, and vestries and sometimes transepts and mortuary chapels. The additional chambers may be part of the original plan, but in the case of a great many old churches, the building has been extended piecemeal, its various parts testifying to its long architectural history.
