St Mark's Campanile (Italian: Campanile di San Marco) is the bell tower of St Mark's Basilica in Venice, Italy. It is the tallest structure in Venice and is colloquially termed "el paròn de casa" (the master of the house). It is one of the most recognizable symbols of the city.

Located in Saint Mark's Square, Venice's former governmental centre, the campanile was initially built as a watch tower to sight approaching ships and protect the entry to the city. It also served as a landmark to guide Venetian ships safely into harbour. Begun in the early tenth century, the tower was slowly raised in height and acquired a belfry and a spire in the twelfth century. In the fourteenth century the spire was gilded, making the tower visible to distant ships in the Adriatic. The campanile reached its present height of 98.6 metres (323 ft) in 1514 when the belfry and spire were completely rebuilt on the basis of an earlier design by Giorgio Spavento. Historically, the bells served to regulate the civic and religious life of Venice, marking the beginning, pauses, and end of the work day, the convocation of government assemblies, and public executions.

The campanile stands alone in the square, near the front of Saint Mark's Basilica. It has a simple form, recalling its early defensive function, the bulk of which is a fluted brick square shaft, 12 metres (39 ft) wide on each side and 50 metres (160 ft) tall. The Renaissance belfry above is topped by an attic with effigies of the Lion of St. Mark and allegorical figures of Venice as Justice. The tower is capped by a pyramidal spire at the top of which there is a golden weather vane in the form of the archangel Gabriel.

The historical tower collapsed in 1902. The actual campanile is a reconstruction completed in 1912.

The Magyar raids into northern Italy in 898 and again in 899 resulted in the plundering and brief occupation of the important mainland cities of Cittanova, Padua, and Treviso as well as several smaller towns and settlements in and around the Venetian Lagoon. Although the Venetians ultimately defeated the Magyars on the Lido of Albiola on 29 June 900 and repelled the incursion, Venice remained vulnerable by way of the deep navigable channel that allowed access to the harbour from the sea. In particular, the young city was threatened by the Slavic pirates who routinely menaced Venetian shipping lanes in the Adriatic.

A series of fortifications was consequently erected during the reign of Doge Pietro Tribuno (in office 887–911) to protect Venice from invasion by sea. These fortifications included a wall that started at the rivulus de Castello (Rio del Palazzo), just east of the Doge's Castle, and eventually extended along the waterfront to the area occupied by the early Church of Santa Maria Iubanico.[note 1] However, the exact location of the wall has not been determined nor is its duration beyond the moment of crisis indisputable.[note 2][note 3]

Integral to this defensive network, an iron chain that could be pulled taut across the Grand Canal and impede further access was installed at the height of San Gregorio. In addition, a massive watch tower was built in Saint Mark's Square. Probably begun during the reign of Tribuno, it was also intended to serve as a point of reference to guide Venetian ships safely into the harbour which at that time occupied a substantial part of the area corresponding to the present-day piazzetta.