The area has been inhabited by the Illyrian tribe of Dalmatae and Delminium was a town established by them in present-day Tomislavgrad. Daelminium was situated on the site of today's Roman Catholic basilica, named after the first Croatian saint, Nikola Tavelić.
The area of Tomislavgrad was populated even before Illyrians arrived, as attested by a few remains of polished stone axes dating from the Neolithic (4000 BC – 2400 BC). Similarly few remains date from the ensuing Bronze Age (1800 BC – 800 BC): 34 bronze sickles, 3 axes and 2 spears found in Stipanjići and Lug near Tomislavgrad, and a bronze axe found in Letka, were kept at the archaeological collection at the monastery in Široki Brijeg, which was destroyed in a fire at the end of World War II. Only one sickle and one axe survived the blaze. Those findings attest that the population of the area at the time were cattlemen, farmers and warriors.
The material remains of Illyrians are much more abundant. On the slopes of the mountains which circle Tomislavgrad, Illyrians built a total of 21 forts which served as watchtowers and defensive works. There are also many Illyrian burial sites dating from the Bronze and the Iron Age to the Roman conquest. The grave goods recovered include jewellery and other items. Apart from Illyrians, other inhabitants of the area included Celts, whose incursions into the Balkans began in 4th century BC. They brought higher culture, crafts and better weapons. The Celts were few in number and were soon assimilated into the Illyrians.
As Romans conquered the territory of the Illyrian tribe Ardiaei to the south, the Delmatae and their tribal union were among the last bastions of Illyrian autonomy. Dalmataes attacked Roman guard posts near the Neretva, Greek merchant towns, and the Roman-friendly Illyrian tribe Daorsi. They upgraded their settlement into a strong fort and surrounded their capital with a ring of smaller forts. The reports of writers from that time say that Delminium was a "large city", almost inaccessible and impregnable. It is assumed that at this time 5,000 Dalmataes lived in Delminium.
In 167 BC the Illyiran forts were unable to stop Roman legions; after the Romans conquered the whole Adriatic coast south of the Neretva and after the state of the Ardieaei was destroyed, the Dalmatae were unable to avoid conflict with Romans. In 156 BC, the first conflict between the Dalmatae and the Romans took place, ending the following year in defeat for the Delmatae. Roman generals Figulus and Cornelius Scipio Nazica conquered, destroyed and burned Delminium, reportedly firing burning arrows at wooden houses. After various revolts led by the Dalmatae and three wars between them and Romans, their resistance was finally quelled in the Great Illyrian revolt that ended in 9 AD.
After Roman conquest of Delminium, Romans started building roads and bridges. Roads that led to mainland of Balkans from Adriatic coast in Salona (Solin) and Narona (Vid near Metković) crossed in Delminium (Tomislavgrad). Remains of those and other Roman roads are still in existence. Romans introduced their culture, language, legislation and religion. For next 400 years Delminium was in peace.
After Romans finally defeated Dalmataes, Tomislavgrad was almost abandoned. There was also, for some period, a military crew of Romans stationed there to keep Illyrians under control. Romans started to rebuild Delminium in 18 and 19 AD in time of emperor Tiberius. During that time, center of city was built, a Roman forum. This forum was built on possession of present-day Nikola Tavelić basilica. In 1896 Fra Anđeo Nunić discovered various sculptures of Roman pagan deities, fragments of pagan sarcophagi, and fragments of columns of medieval Christian church. From all those discoveries, most prominent are two votive monuments and altars dedicated to goddess Diana, one altar dedicated to native Illyrian god Armatus and one votive plate dedicated to goddess Libera. Later, relief of goddess Diana was also found and one relief of Diana and Silvanus together. Also, new pagan altars, fragments of sarcophagi, clay pottery, parts of columns, and various other findings from Roman and early medieval age were found. This led to conclusion that on place of present-day Catholic graveyard "Karaula" (which was previously an Ottoman military border post and guardhouse) was Roman and Illyrian pagan sanctuary and graveyard.
In 1969, a tablet, which was part of an altar, was found near village Letka. It is dedicated to the Roman god of war, Mars by a soldier of the 9th Legion. A year later, in village Prisoje, a Christian font was found and part of a tomb, made by father Juvenal to his son Juvenal.
After Roman Empire
Roman Delminium survived for two centuries during the large migrations. During that time, Delminium was partly damaged and somewhere in middle 5th century, Roman forum was destroyed. After collapse of the Roman Empire in 473, Delminium was under short rule of Goths between 493 and 537. After Delminium came under Byzantine Empire in 573, the city was fully recovered. But, soon it was again highly damaged by new arrivals and deducted from the Byzantine Empire in 600.
- Wilkes, J. J. The Illyrians, 1992, ISBN 0-631-19807-5, Page 188, "... after whom the Roman province Dalmatia was named, their own name being derived from their principal settlement Delminium near Duvno. Beyond the Dinara, Delmatae occupied the plains of Livno, Glamoc, and Duvno, ..."
- Wilkes, John (1995). The Illyrians. The Peoples of Europe. Wiley-Blackwell. p. 244. ISBN 0-631-19807-5.
- Stipčević, Aleksandar (1977). The Illyrians: History and Culture. History and Culture Series. Noyes Press. p. 197. ISBN 0-8155-5052-9.
- Rathbone, p. 597.
- Wilkes 1992, p. 188.
- (Croatian) Bagarić, Ivo. Duvno: Povijest župa duvanjskog samostana. Sveta baština. 1989
- Bagarić 1980, p. 9.
- Bagarić 1980, p. 10.
- (Croatian) Bagarić, Ivo. Duvno - Short Monograph. Župni ured sv. Franje Asiškog, Bukovica. 1980.
- Bagarić 1980, p. 12.
- Bagarić 1980, p. 13.
- Bagarić 1980, p. 14.