Barby is located immediately north-west ofRethel and immediately south-east ofChâteau-Porcien. Access to the commune is by the D926 road from Rethel which passes through the heart of the commune and the village before continuing north-west to Château-Porcien. The D946 from Rethel passes through the north of the commune as it goes north-west toSeraincourt. The commune is entirely farmland.[5][6]
TheAisne river passes through the south-east of the commune forming a small part of the south-eastern border as it flows west to eventually join theOise atCompiègne. The Vaux river flows south, forming the western border of the commune, to join the Aisne just outside the south-western tip of the commune. TheRuisseau de Bourgeron flows from the north-east through the commune and the village and joins the Aisne on the southern border. TheCanal des Ardennes is parallel to and south of the Aisne and forms a small portion of the southern border of the commune.[5]
July and August are very hot and dry with temperatures up to 38 °C. Even so, rainfall is more frequent in summer, but the winters are shorter and less severe. The cold weather lasts only from October to March which favours corn crops and especiallyKitchen gardens.
A Wayside Cross on the presumed site of the birthplace of Jean de Gerson
Excavations have uncovered aBronze Age tomb in Barby and the village is traversed by the oldRoman road from Rethel to Château-Porcien.
The village of Gerson was located on the current territory of the commune in the Middle Ages but is now gone. It was at Gerson thatJean Charlier de Gerson, Chancellor of theUniversity of Paris (nicknamedDoctor Christianissimus), was born in 1363. A Wayside cross marks the place which traditionally is his birthplace. The commune named the Rue Gerson after him and the parish built a monument in the church during its construction in 1880 or 1881.
Barby appears asBarby on the 1750Cassini Map[7] and the same on the 1790 version.[8]