When you hold the fort, it means that you take care of a place when the person normally in charge is away.
When Michael, the boss, went on holiday, he asked me to hold the fort at our company.
I'm just going out to the shops for 20 minutes, can you hold the fort?
Another phrase which uses the word 'fort' is to be like Fort Knox. If you say a building or place is like Fort Knox, you mean it is very well protected and difficult to enter or leave.
My office is like Fort Knox. You need to bring your ID or they won't let you in.
Bagpipes were designed to be played outside, and the sound they make can be heard up to ten miles away. In the past they were used when Scottish armies went to battle and their music could be heard above the loud sounds of fighting.