According to the archaeologic find the settlement dates back to the Paleolithic period (40.000-12.000 years ago).
In 9th century BC the Piceni formed two settlements on the Piceno hill and on the Monte San Pietro.
Considering its impregnability, in 157 BC the Romans founded here a colony.
During the Middle Ages the town maintained its importance.
Conquered by the Lombards in 728 it passed to the Franks in 774 when Charlemagne annexed all the Lombard territories and donated Osimo to Pope Adrian I.
Osimo was one of the first one Communes and afterwards it entered the Papal States.
Subdued by the Frenches in Napoleonic era, Osimo returned under the papal rule at Napoleon’s fall.
After the plebiscite on November 1860 it entered the Kingdom of Italy.
Placed on the Gomero, the highest hill of the town, It is the main church of Osimo.
Built in 5th century on the remains of a Roman temple by the bishop San Leopardo who, according to the legend, dedicated this church to Santa Tecla.
The legend tells also that it was rebuilt by the bishop San Vitaliano in 7th century.
Historical documents prove the enlargement decided by the bishop Gentile who (end 12th-beginning 13th century) built the present presbytery, the crypt, the apse and the prothyrum.
At the end of 13th century the bishop Giovanni Uguccione altered its structure introducing Gothic elements.
Other renovations date back to 15th-17th century.
In the second half of 1800 an insane renewal modified and often destroyed several ancient works.
The cathedral became National Heritage in 1940.
In the interior there are many notable works (see the following links).