The door had been nailed up and so had the window, and entrance could only be effected by scrambling up on the flat roof, and dropping through a hole which had been made there for that purpose.  Even that hole could be closed by a hatch in time of need, and the besieged could lie snugly inside and listen to the heavy firing without, secure in the knowledge that as long as he chose to remain there none of the besiegers could touch him.  But then his flag would be in danger; and by their rules of warfare, if the flag were captured or shot down, the fort was held to have capitulated.