The Venetian Republic based its revenue on the trade between the East and the West. Therefore its territory comprised a very elongated series of possessions along this trading route; in the period of its greatest extent it stretched from northern Italy (Lombardy) to Cyprus. The ports with their infrastructure were vital for the marine traffic along the coast. Here the ships could be supplied, repaired, or given shelter from a storm. In order to secure the distant parts of its territory, in particular the towns with ports, the Venetian Republic constructed fortifications and erected various military and public buildings such as arsenals, cisterns etc.
The greatest Venetian enemy in the early modern times was the Ottoman Empire, threatening and occupying its possessions. From the mid-15th to the early 18th century, the two states fought seven wars. Although in these wars the Venetian Republic lost some of its possessions and gained others, the Turkish empire was gradually driving it out from the eastern Mediterranean.
In Jančić’s period, of special interest are the fortresses built between the mid-17th and the mid-18th century – those which were considered modern, and particularly those on which Jančić left his mark. Fortifications were regularly built in times when there was a danger of war. During the said period three Venetian-Ottoman wars took place: the War of Candia (1645–1669), the Morean War (1684–1699) and the Second Morean War (1714–1718).
Important Dalmatian fortresses of the time are those of Šibenik and Split, built at the start of the War of Candia as separate forts on the hills above the towns. Above Šibenik there are two forts, S. Giovanni and Barone, and above Split there is the fort Gripe. Since the distance of these positions did not pose any difficulty for the enemy cannons, they had to be secured in order to prevent the Turks from threatening the towns from there. These fortifications had cannon embrasures and stronger ramparts on the sides opposite the towns, from where Ottoman attacks were expected.
During the next conflict, the Morean war, the Republic took Knin and decided to modernise and extend it, thus ranking it among the most important Venetian fortresses. Knin ultimately became the only strong Venetian fortress in Dalmatia at a distance from the sea. According to the available sources, it was the only site in Croatia on which Jančić was engaged.
In this selection of late Venetian fortifications, let us also mention two Greek fortresses. The town of Corfu on the island of the same name was of key importance for the Venetian Republic not only as a stop on the naval route, but because of its position that allowed control over the access to the Adriatic Sea. As the Turks progressively occupied the eastern Venetian possessions, the remaining ones – including Corfu – thus became even more valuable. The Ottoman forces unsuccessfully tried to conquer Corfu several times, and it remained in Venetian possession. Jančić knew Corfu well, being permanently engaged there.
The case is different with the fortifications of Napoli di Romania (Gr. Nafplio) in the Peloponnese. Venice returned this Greek peninsula under its control during the Morean war, and then modernised and built a number of important fortifications. As the capital of the Peloponnese (Morea), Napoli was the most significant one among them. High above the town there too was a position that presented a potential threat; it was from there that the Venetians had bombed the town while it was still in Turkish possession. That is why the Venetian Republic now erected a new complex fortress there, designed by Jančić. However, by 1715 the work had not been completed, and the fortress was seized by the Turks.