Gaudí devised a Sagrada Familia of great height, visible from all Barcelona, with eighteen towers: twelve for the apostles, four for the evangelists, and the crests of Jesus and Mary. The heights vary: towers of the Nativity (98.40 meters and 107 meters), Passion (107.40 meters and 112.20 meters), Glory (112.20 meters and 120 meters), Evangelists (135 meters), Virgin (138 meters), and Jesus (172.50 meters).

The Nativity towers have a square base, becoming circular with balconies and figures of apostles. They are supported by sandstone ribs with vertical openings and inclined pieces to protect from water and to diffuse the sound of bells.

The tops of the towers vary: polychrome Venetian mosaic pinnacles with coats of arms, symbols and initial letters of apostles. Inscriptions such as Hosanna, Excelsis and Sanctus are repeated in colors related to the Trinity. Inspired by cat's claws, the pinnacles represent each apostle with zodiacal constellations.

The towers function as bell towers with eighty-four common and tubular bells: Nativity (percussion), Passion (resonant organ) and Glory (tuned in E, G, C). Gaudí studied the acoustics meticulously. The towers house spiral staircases inspired by sea shells called turrets.