Today’s territory of Kostanjevica na Krki was already colonized in prehistoric times, which is proven by the two stone artefacts from the Palaeolithic period found near the Cistercian monastery and the wooden boat, found 4 m deep in the river near Kostanjevica. At the moment, there’s still no evidence of colonization in the Neolithic Period and the Bronze Age, but there are some archaeological sites from the late Bronze Age or the Urnfield culture found in Dobe. The 60cm high urns filled with remains of the dead were a peculiarity. There was a bronze bracelet from the late Iron Age. The closest Hallstatt fortress was Stari grad pri Podbočju with a Hallstatt graveyard nearby. A Hallstatt graveyard was also found near the village Sajevce. Under the Roman authority, in the 1st century BC, the first habitants came. There were some finds as coins, fibulas, blades, a stone lion near the old castle and its hillsides, an antique tomb in the village Sajevce ant 2 Roman stone plinths and a piece of a gravestone on the Kostanjevica island. The first appearance of Slovenians is confirmed by an Old Slavic small pot that was found in the river Krka. There is also evidence of the existence of an Old Slavic settlement from the 10th century.

Although, the territory was already colonized in early periods, Kostanjevica was at its peak in the Middle Ages. In 1091, the settlement owned by the counts Breže-Selški was first mentioned. At the beginning of the 13th century, Kostanjevica had a revival as the dynasty Speinheim began gaining lands near the lower part of the river Krka, on strategically important territories boarding on the Kingdom of Hungary. In 1215, Kostanjevica already had an important role in this region, which is evidenced by its own coin mint. The coin states “Civitates Landestrost”, which means the town Landestrost and is the first medieval name for Kostanjevica, meaning trust and courage of the land. The town’s development was promoted by the opening of the Cistercian monastery nearby in 1234, which also grew his importance and making it in 1252 the first town in Dolenjska to gain the town rights. Kostanjevica na Krki had special privileges as town, like its own law, commerce, organized fairs, collecting bridge tools, etc. The town was led by 3 judges and from the town council 12 people under oath. The oldest preserved record of the Kostanjevica town law dates from 1307 and it was an example for gaining town rights to other places in Dolenjska and Bela Krajina. This prosperous time lasted until the second half of the 14th century and was followed by a period of regression for the town. The Turkish invasions, the immigration of Uskoks, floods, fires and the founding of new towns nearby (Brežice, Novo mesto, Krško) weakened the town’s strength that didn’t follow the imposed growth in the 13th century. Kostanjevica was owned by a number of aristocratic families, as the Counts Breže-Selški, Speinheim, Ortenburg, Celje and the Habsburgs. We first came across the Slovenian name Kostanjevica na Krki in 1615. Despite the town’s regression, Maria Theresia renewed its town rights in the second half of the 18th century and selected it as an administrative centre. In 1786, after the closing of the monastery, the spaces went to the forest administration and the court. In the 19th century, the social life of Kostanjevica was revived. The town guards, the fire department and the town band were founded. The town started to expand from the island to the land. In 1906, a new school was built that still stands today and host a gallery activity. The year 1928 represents the cradle of an organized production of Cviček with the founding of the wine cooperative Kostanjevica, situated in the old Cistercian monastery.

Today, Kostanjevica na Krki is a municipality with 2.500 residents who work mostly in the nearby towns of Novo mesto, Krško and Brežice. Despite the fact that people work, agriculture is still a main side activity. Tourism is also becoming an important industry in the region of the river Krka.