Since its foundation, the important geographic position of the Abbey, with its rich soil, drew upon it the interest and the greediness of warmongers. In the XI century it was engaged several times in the wars between Rome and Tuscolo.

The last devastation (1482) made by the troops of the duke of Calabria and then by the Orsini and Colonna families, finally convinced Cardinal Giuliano della Rovere – Iulianus Cardinalis (later Pope Julius II) at the end of the XV century to erect protections around the Abbey. And so the fortress were raised: the towers, the look-out posts, the moats, the embattled walls with the draw-bridge. The architects were Baccio Pontelli (1450-1494) and Antonio da Sangallo (1463-1534). This imposing work gave the Abbey the majestic and strong appearance that it still has. The building up of this fortress happened between 1483 and 1491.

In 1492 Giuliano della Rovere, opposed by Pope Alexander VI, left away taking refuge in France and the Castle of Grottaferrata passed temporarily under Fabrizio Colonna by the guide of Alfonso, King of Naples.