It then belonged to the estate of Farra, held by the Patriarchs of Aquileia. From 1420 onwards their lands were gradually conquered by the Republic of Venice, annexed and incorporated into the Venetian Domini di Terraferma in 1473. The Venetians fortified Gradisca as a bastion against Ottoman raids, then part of a massive defence line along the Isonzo River relying on plans designed by Leonardo da Vinci.