Omiš was a small independent medieval county.
It had a developed system of attack and defense.
Omiš pirates of that time (better to say privateers) were not barbarians. They were organized in the county of hereditary Counts Kačić, with the capital in Omiš. They fought for their independence during very difficult historical time, surrounded by forces like Republic of Dubrovnik, Venice, Kingdom of Hungary and Byzantium.
Prof. Solomon often mentions Venetian saying: – „Barbarians were those who didn't know how to swear in Latin“. But Omiš pirates had written contracts in Latin. On the stamp is written “Nikola Lord and Count”.
Horseman with a sword means that Nikola was an independent ruler. Venice, Dubrovnik, Kotor and other had to pay fees for free sailing through the Adriatic Sea. And also, they had the fastest ships of that time.
For that purpose Omiš pirates built and used their FORTIFICATIONS that included: CITY WALLS, with a small canal called FOŠA, and Bastion for defense of the southern part of the city. FORT MIRABELA was used for protection from the north, and FORT FORTICA was used for observing the sea and protected from the attacks from the mainland. And the most interesting for us today, was MOSTINA underwater fortification in the delta of the river Cetina. The Mostina was made for two reasons: a) First, as protection from the enemy ships that were following or chasing sagittas: while sagitta would have passed over the Mostina (because of shallow bottom), the enemy ship would get stuck. This was very specific AND UNIQUE DEFENSE SYSTEM ON the MEDITERRANEAN. b) The second reason was to protect city from the strong southwest wind.