Would someone explain pickets to me please? I understand the reason for posting pickets around the army camps, but don't know much about the structure of a picket line. I recently read that picket lines are made up of three...I guess they could be called "tiers." Sentries, picket supports and was referred to as "grand reserves." I don't entirely understand those terms, and the differences (if any) in the duties of each...I guess I'll have to refer to them as "classifications." Just what does picket support mean, how do these men differ from sentries, and where do the grand reserves come into the equation? Generally speaking, how far apart are sentries placed? Do they surround the entire camp? I would suppose that the number of soldiers needed as pickets would depend on the size of the camp and whether all four sides were vulnerable to attack, but is there any sort of general number of soldiers who would be on picket duty at any given time?