The author presents in this study the development of sea-trade and seatraffic, in places on both shores of the Adriatic Coast, he also established the number of ships which are mentioned in sources available for this period (there were as many as 620 ships), and he also made a survey of ownership of ships. The core of this study is the presentation of forms and technique of sea-trade and maritime law (business associations, hiring of ships). Ship-building is treated especially in detail, and the study is concluded by the description of the position of sailors.