"as the old knights of the Cross"
The Battle-of-Ager-Sanguinis
Public DomainThe Battle-of-Ager-Sanguinis - Credit: wikimedia commons

“Knights of the Cross” may refer to a specific order of knights whose emblem was a cross, such as the Teutonic Knights, who helped Christians on their pilgrimages to the Holy Land, and who set up hospitals there, or the Knights Templar, a Christian military order which fought in the Crusades. However, it seems more likely that Van Helsing is  referring to all knights who fought in the various Christian Crusades in the Holy Land in and near Jerusalem.

The Crusades were a series of medieval religious wars sanctioned and blessed by the Pope, with the aim of reasserting Christian control of the holy sites at Jerusalem. In other words, Van Helsing believes that they are on a mission from God to rid the world of Dracula’s evil.