Roman Legionaries Vs. Medieval Heavy infantry

[LCorneliusScaeva]

If the romans were to have fought later in history againist full armoured Knights etc. what would have been the outcome?

Here's another technique known to the Romans that would have worked with Knights on horseback:

[from good old wikipedia]
The late Roman writer Vegetius, referring in his work De Re Militari to scythed chariots, wrote:

The armed chariots used in war by Antiochus and Mithridates at first terrified the Romans, but they afterwards made a jest of them. As a chariot of this sort does not always meet with plain and level ground, the least obstruction stops it. And if one of the horses be either killed or wounded, it falls into the enemy's hands. The Roman soldiers rendered them useless chiefly by the following contrivance: at the instant the engagement began, they strewed the field of battle with caltrops, and the horses that drew the chariots, running full speed on them, were infallibly destroyed. A caltrop is a device composed of four spikes or points arranged so that in whatever manner it is thrown on the ground, it rests on three and presents the fourth upright.