The original city of Syracuse stood on the island Ortyga with some structures around the Agora in the mainland before the Sicilian Expedition in 415 BC, when walls were built around the Tycha and Archadina areas.
After Dionysius finished adding to the existing structures, Syracuse possessed walls with the greatest circuit in the Greek world.

Dionysius had rebuilt the walls around Ortygia so that they surrounded the whole island and the isthmus connecting the mainland with a robust wall complete with towers at regular intervals which were strongly built.
The isthmus had docks on the west side and the little harbour, Laccius on the east side.
Screens and walls were put up to enclose Laccius, and it could accommodate 60 triremes, and a gate was provided between the sea screens that would let one trireme pass at a time.
Two castles were also built on Ortygia, one near the isthmus, which was the home of Dionysius, and one further south.
Two walls were built on the isthmus itself, one separating the island from the isthmus and one the mainland from the isthmus.
A series of five gates built on the isthmus, the Pentaplya, controlled access between the mainland and Ortygia.

Dionysius then populated the island of Orytiga with loyal mercenaries and close supporters.
A massive castle with underground structures was built at Euryalos which guarded the main access to the route to the Plateau.
He incorporated the walls built during the Athenian Expedition for settling the people in Achradina.
The walls around the plateau, made entirely of stone may have had a thickness between 2 and 4.5 meters and a height of 6 meters.
The original city of Syracuse stood on the island Ortyga with some structures around the Agora in the mainland before the Sicilian Expedition in 415 BC, when walls were built around the Tycha and Archadina areas. After Dionysius finished adding to the existing structures, Syracuse possessed walls with the greatest circuit in the Greek world.
Dionysius had rebuilt the walls around Ortygia so that they surrounded the whole island and the isthmus connecting the mainland with a robust wall complete with towers at regular intervals which were strongly built. The isthmus had docks on the west side and the little harbour, Laccius on the east side. Screens and walls were put up to enclose Laccius, and it could accommodate 60 triremes, and a gate was provided between the sea screens that would let one trireme pass at a time. Two castles were also built on Ortygia, one near the isthmus, which was the home of Dionysius, and one further south. Two walls were built on the isthmus itself, one separating the island from the isthmus and one the mainland from the isthmus. A series of five gates built on the isthmus, the Pentaplya, controlled access between the mainland and Ortygia.
Dionysius then populated the island of Orytiga with loyal mercenaries and close supporters. A massive castle with underground structures was built at Euryalos which guarded the main access to the route to the Plateau. He incorporated the walls built during the Athenian Expedition for settling the people in Achradina. The walls around the plateau, made entirely of stone may have had a thickness between 2 and 4.5 meters and a height of 6 meters.
Siege of Syracuse (397 BC)