What were the biggest problems faced by the early byzantine engineers, as the city of constantinople began to grow?

The biggest problem faced by the early Byzantine engineers was that the growth of the city far outpaced the growth in its resources, so water and food had to be brought from the outside.The city was also under constant threat of invasion by Germanic tribes to the north and east and needed to be heavily fortified, making moving resources into the city a bit more difficult.

What does that mean mon