Since the arrival of Croats in the Kaštela area, land ownership has emerged as the main driver of social processes and conflicts in the developed and late Middle Ages. Submissive to various authorities who ruled over the area for a certain period, Trogir and Split tried to appropriate as much of the Kaštela field as possible, and as a result of their expansionist aspirations, the field was divided into Split and Trogir, ie Dilat and Podmorje. This period was marked by tensions and occasional conflicts between the two communes, Trogir and Split, and the greatest damage was suffered by the farmers who lived in the Kastela area. A relatively peaceful period ensued with the establishment of Venetian rule in Dalmatia as Venice encouraged cooperation between cities for its own benefit. As the Turkish danger approached, the communes of Split and Trogir, on their own initiative, with the support of the Venetian authorities, built defensive fortifications, castles, in order to protect their estates in Kaštelansko polje. By building castles, the nobles of Trogir and Split committed themselves to the construction of fortified settlements around the castle and thus marked the beginning of the existence of the castle as we know it today. The paper will analyze the origin and development of Kaštel Stari, Kaštel Novi, and Kaštel Štafilić, as well as their functioning and socioeconomic relations in them. With the erection of castles and fortified settlements around them, the topographic picture of the Kaštela field changed. Instead of scattered Podkozjak villages, coastal, fortified settlements were built, with a relatively strict and regular internal layout. The settlements were protected from the land sides while the seaside served as an exit in case of danger. Although the settlements could not withstand strong Turkish attacks, they served a purpose and provided relative protection to their settlers. Since the nobles of the surrounding massifs built fortifications and their settlements at their own expense, it was evident that in the following centuries, they would, through various peasant obligations, reimburse their expenses. Over time, the gratitude of the population for the shelter was less and less, and the desire for independence is growing, there are more and more conflicts between farmers and nobility, and fraternities stand out as representatives of the regiment and new bearers of social change in these villages.