Great Structures - Lantern towers: Illuminating the heart of cruciform churches

In church architecture, a lantern tower rises directly above the central intersection of four arms in a cross-shaped layout. Equipped with openings that direct natural light down onto the crossing floor, these structures are frequently built in an octagonal plan, enhancing the decorated interior of the dome above. A related Italian concept, known as a tiburio, places a windowed polygonal lantern atop a dome, derived from a Medieval Latin word meaning a hut, which relieves structural weight while admitting light.

Source: Wikipedia