In the Sand Reckoner what does Archimedes realize about the great harbour

Archimedes found the Great Harbour enclosed with walls needed for the protection of the city. Syracuse was at war. It now belonged to the navy and they kept an eye on all activity in the harbor. It was different from when he left. It was a far cry from the openness and freedom the world beyond the Mediterranean offered.

he realized that Syracuse, the great port, was then only a red and gold stain between green hills; it seemed as if time had vanished in the sand, and now Syracuse appeared before him. There, in the port of the richest and most powerful city of all the Greek cities of Sicily, he saw nothing but walls, the city was at war, and he, being the only male of his family, his duty was to protect and to support his family, in what would surely be a terrible war.