The gate was high and yet the way through was narrow so that two horses could
not pass at once. 
It was made like a trap for a rat, for as soon as anything stepped on a hidden
spring underneath the gate, the portcullis
would drop and its iron prongs would cut and mangle whoever was beneath.
The wounded knight knew his way and dashed straight through, but Yvain's horse trod on the hidden spring just as Yvain reached forward to grab his enemy's saddle and pull him from his horse. The gate came crashing down, slicing off Yvain's spurs level with his heels and chopping his horse in two.
Yvain was lucky to be leaning so far forward, for he was not hurt at all but fell to the ground. The Knight of the Spring escaped through another gate just ahead, and it clanged shut behind him.
