Replace the word "stronghold" in the sentence with a synonym.
The city was known for its economic stronghold, which gave it a unique advantage.
The city was known for its economic fortress, which gave it a unique advantage.
Complete the following task based on the instruction and optional input provided.### Instruction:
Replace the word "stronghold" in the sentence with a synonym.

### Input:
The city was known for its economic stronghold, which gave it a unique advantage.

### Output:
The city was known for its economic fortress, which gave it a unique advantage.