Tower of San Dionisio, Mudéjar defensive tower in Jerez de la Frontera, Spain.

The Tower of San Dionisio, also called Torre de la Atalaya, Torre del Reloj or de la Vela, is a civil tower attached to the Church of San Dionisio; its base is the old Sagrario chapel. It has two rectangular bodies, with the staircase in the narrower one, and is built of calcarenite stone from the Sierra de San Cristóbal. Its exterior is decorated with blind windows of double lobed arches, muqarnas capitals and tracery, and it carries a bell gable with a bell.

The council built the tower in the mid-15th century to house Jerez's first clock and to give warning by smoke signals from bonfires lit when danger approached. In the early 16th century it became a watchtower against Berber raids on the Cádiz coast, when light North African vessels came to abduct people and demand ransom for their release.

The tower's name comes from its role as a watchtower: smoke from bonfires signalled danger, and in the early 16th century it warned of Berber raids on the Cádiz coast, when light vessels from North Africa came to abduct people and demand ransom. Hence the saying that there were "Moors on the coast".

The tower is attached to the Iglesia de San Dionisio and rises above Plaza Plateros, not Plaza del Arenal. It is a municipal civil building, separate from the church, and can only be viewed from the outside; consolidation work took place in 2017 and two pieces of its exterior cladding fell off in 2021. A deeper intervention to open it to visitors was presented as a project in 2018.

The tower's warning role gave rise to the saying "hay moros en la costa": smoke from bonfires signalled Berber raiders from North Africa, whose light boats came to kidnap people and demand ransom for their release. The tower is municipal property, listed separately from the church it adjoins under code RI-51-0004318.