GUARD YOURSELF LIKE A FORTIFIED CITY
Nagaram yatha paccantam guttam santara bahiram
Evam gopetha attanam khano ve ma upaccaga
Khanatita hi socanti nirayamhi samappita.
As a border town is guarded both inside and outside, so guard yourself.Let not the opportunity1go by;
for those who miss the opportunity come to grief when they fall into a woeful state. 
In the first month of their stay in a border town, some bhikkhus were well provided for and well looked after by the townsfolk. During the next month the town was plundered by robbers and some people were taken away as hostages. The people of the town therefore, had to rebuild and protect their town. Thus, they were unable to attend to the needs of the bhikkhus as much as they would have liked to. So the bhikkhus had to fend for themselves. At the end of the vassa, those bhikkhus went to pay homage to the Buddha at the Jetavana monastery in Savatthi. They told the Buddha that due to the difficulties faced by the people, they also had to undergo hardship for the last two months of the vassa. So the Buddha advised them, 'Bhikkhus, don't keep thinking about this or anything else. It is always difficult to have a carefree, effortless life. Just as the townsfolk guarded their town, so also a bhikkhu should be on guard and keep his mind steadfastly on his body.'
- The birth of a Buddha, a congenial habitation, a healthy body, the possession of right views, etc.