A long, long time ago, people didn't have fancy buildings with strong walls like we do now. So, when people needed to stay safe from their enemies, they built special areas called forts. These forts were like really big houses that had a lot of rooms, but most importantly, they had very high walls all around them to protect the people inside from any bad guys outside.
Now, imagine that you have to build one of these forts. You will need many people to help you because it is a lot of work! They will have to dig deep holes in the ground and fill them with rocks and dirt to make strong walls. They will also pile up large rocks on top of each other to make the fort's walls even stronger. The walls will have to be very high so that nobody can climb over them.
But you can't just have really high walls and leave it at that. You also need to worry about how people will enter and leave the fort. So, you will need to make special gates that can only be opened by people who know the password, or by the guards who are watching the gates. These gates will also be very strong, so that nobody can easily break them down.
When you're done, you will have a very strong, safe place for people to live in. And when the bad guys come to attack, they won't be able to get in because of the high walls and strong gates. This is what is called a sangar, or a fortification!