Big rondella, Medieval fortification in Castle Hill, Budapest, Hungary.

The Big Rondella is a circular fortification on Castle Hill with thick stone walls and multiple bastions. This structure formed part of the layered defense system and features gun ports and cannon positions.

The exact construction date of the rondella is unknown; it may have been built under King Matthias (1458–1490) or later, under John Zápolya, but before 1541. It is absent from a drawing of the castle made around 1467 but appears on an engraving from 1541, the year Buda was captured. In 1686, during the recapture of Buda, the besiegers' artillery breached its wall and the attackers entered through the gap. Before 1945 the medieval wall was largely buried; archaeological research preceded its restoration in the 1950s.

The fortification structure contains architectural elements that demonstrate medieval Hungarian military engineering and construction techniques from different periods.

Visitors reach the fortification on foot from the castle entrance or via the historic pathways climbing the hill. The terrain is steep, so comfortable shoes and drinking water are recommended.

During the 1950s restoration, the 13th-century foundations of the so-called Kelenföld Gate were found more than 5 metres below the rondella's present level. The original rondella was probably built after this gate was demolished and its site was enclosed.