Thousand of knights?
Viliges du Roi Charles VII, by Martial d’Auvergne.
King Perion brought 3,000 knights from Gaul. From Spain came 2,000. From Constantinople, 8,000. Great Britain, 6,500. And 10,000 from Rome.
How realistic were these numbers?
In about 1423, Venice tried to document the estimated power of the countries in Europe and parts of Asia, according to an article at Medievalist.net. Among the estimates:
Brittany: 8,000 horsemen
The Papacy: 6,000
So the fighting forces of the late Middle Ages were larger than those in this story. Of course, as the story says, the events in Amadis of Gaul occur “not many years after the passion of our Redeemer and Savior Jesus Christ” – that is, long, long ago in the fantasy past.
But given that it really was set in medieval Europe, these emperors, kings, and lords reasonably could have raised the armies described in the story. Garci Rodríguez de Montalvo had served King Fernando in battles against the Kingdom of Granada, so he had some idea of warfare. The exact battle techniques, however, tend to be from earlier medieval times, perhaps because they are more dramatic and offer more chances for individual fighters like Amadis to excel.
This is fiction, not a documentary, but the fighting that is soon to come has some basis in reality. Big armies are about to fight – two armies, with a third waiting to ambush the victor.