what does it mean?

[bartholomew]

The knight stopped and looked at the soot-stained rushes at his feet.

What is rushes?

[Clanad]

'rushes' in this context are reeds or bull rushes gathered from wetland areas.  They are also called cattails.  They were used in medeival times as covering for stone floors.  Once they were sufficiently dirty, they were removed and replaced... As can be imagined, the rushes became quite filthy before they were removed...