《明史·志·卷六十六》
那以后边地警急，于是合并轮番上京的军队为一班，五月前往京城，十一月放还，每年秋季防守现有军队五六万。
其后边警棘，乃并番上军为一班，五月赴京，十一月放还，每岁秋防见兵十五六万。
After that, the border was alerted, and the troops who took turns to go to Beijing were merged into one group. They went to Beijing in May and were released in November. There were 50,000 to 60,000 soldiers defending every autumn.