The oldest trace of a vicus or locus of Castellano was found in the Benedictine documents of Conversano. It dates back to 901 and consists of a sales contract of a farm in which "vico Castellano" is mentioned.
Castellano was born as a complex of a few rural houses. Later it became part of the feud of the Norman counts of Conversano and in 1087 it was granted under a full jurisdiction of the Benedictine monastery of the town. This dependence was repeatedly confirmed in the following times.
The village was destroyed and its inhabitants scattered in 1171. Eustasio, abbot in office that time wanted to repopulate the area with vasallage and perpetual colony, entrusting the task to Nicola and Costa who were colonists of Terra d'Otranto and from whom the current population of Castellana derives through an uninterrupted series of generations.
So Castellana was founded in 1171 by Nicola and Costa.
In 1266 pope Clemente IV offered the uninhabited monastery of Conversano to a group of aristocratic nuns of Cisternino who probably had French origins, granting them also the ecclesiastical jurisdiction of the monastery. So the abbess of San Benedetto was given the ordinary power over the clergy and the population of Castellano, becoming that way the prelate. Monstrum Apuliae, the wonder of Puglia, was born.
Ecclesiastical jurisdiction was exercised until Gioacchino Murat, a member of Napoleon's family and the king of Naples, abolished it in 1810.
Civil jurisdiction instead was affiliated from the first half of the 14th century till the first half of the 15th century to the Princes of Taranto and from 1456 onwards to the Counts of Conversano.
A complete transformation of agriculture took place towards the end of 17th century. Extended areas of scrubs and woods were transformed into cultivations with olive groves and opulent vineyards. This way the farmers class, composed of the owners of small properties, increased and consolidated and became the most singular economical characteristic of Castellana. The deforestation, though, was caused by recurrent floods that started to devastate the lowest region of the Castellana area, set in a karst valley with no outlets.
All this caused the frightful floods in 1741 and 1784 which claimed several victims. Only a large hydraulic work put an end to the tragedies in 1913. The 18th century brought with it major transformations of all kinds.