I briefly wondered at the wisdom of leaving a permanently open hole in one's defensive wall, But with this redoubtable entity standing in the opening, and a few guys with bayonets and/or pikes and/or clubs and/or just about anything in their hands there as well, it wouldn't make for an easy entry into the Retrenchment area. Remember, once an attacker got through this, they'd still have to get into the fort itself.