Lucius Domitius Ahenobarbus, who had become proconsul of Gaul, is sent in April 49 to gain control of Massalia (modern Marseille) in order to oppose Caesar.

As Caesar marches to Spain (en route to the Battle of Ilerda), the Massiliots close their gates to him, having allied with Ahenobarbus and the Optimates.

Roused by their hostile actions, he commences a siege against Massallia, leaving the newly raised XVII, XVIII, and XIX legions to conduct the siege.

These are the same legions that will be wiped out at Teutoburg Forest fifty-eight years later.

He also places Decimus Junius Brutus Albinus in charge of his fleet here.

After the siege has begun, Ahenobarbus arrives in Massallia to defend it against the Caesarian forces.

In late June, Caesar's ships, although they are less skillfully built than those of the Massiliots and outnumbered, are victorious in the ensuing naval battle, after which the fleet is confiscated by the Roman authorities.

Gaius Trebonius, Caesar's legatus, conducts the siege using a variety of siege machines including siege towers, a siege-ramp, and a "testudo-ram".

Gaius Scribonius Curio, careless in adequately guarding the Sicilian Straits, allows Lucius Nasidius to bring more ships to the aid of Ahenobarbus.

He fights a second naval battle with Decimus Brutus in early September, but withdraws defeated and sails for Spain.

The Massiliots valiantly defend against the siege machines and works.

They throw down burning pitch and pine-shavings as the Caesarians undermine the foundations of their city walls.

At one point they seem likely to surrender and declare a truce, but at night they cunningly destroy the siege works in a gross violation of the treaty.

They are now near surrender.

At the final surrender of Massallia, Caesar shows his usual leniency and Lucius Ahenobarbus escapes to Thessaly in the only vessel that is able to escape from the Populares.

Afterwards, Massallia loses its independence and is absorbed into the Roman Republic.

During Roman times the city is called Massilia.

John Cassian, while he was in Rome, had accepted Pope Innocent’s invitation to found an Egyptian-style monastery in southern Gaul, near Marseille.

He may also have spent time as a priest in Antioch between 404 and 415.

Whatever the case, he arrives in Marseille around 415.

His foundation, the Abbey of St. Victor, is a complex of monasteries for both men and women, one of the first such institutes in the West, and will serve as a model for later monastic development.

John Cassian had come very late into writing and only does so when a request is made by an important person or persons.

His sources are the same as those of Evagrius Ponticus, who had been among his teachers, but he adds his own personal ideas, which are arranged in extensive collections.

Cassian writes two major spiritual works, the Institutions and the Conferences.

In these, he codifies and transmits the wisdom of the Desert Fathers of Egypt.

These books are written at the request of Castor, Bishop of Apt, of the subsequent Pope Leo I, and of several Gallic bishops and monks.

The Institutions (Latin: De institutis coenobiorum) deal with the external organization of monastic communities, while the Conferences (Latin: Collationes patrum in scetica eremo) deal with "the training of the inner man and the perfection of the heart."

In Books 1-4 of Institutions, Cassian discusses clothing, prayer and rules of monastic life.

Books 5-12 are rules on morality, specifically addressing the eight vices - gluttony, lust, avarice, hubris, wrath, envy, acedia, and boasting - and what to do to cure these vices.

The Conferences, dedicated to Pope Leo, to the bishop of Frejus, and to the monk Helladius, summarize important conversations that Cassian had had with elders from Scetis about principles of the spiritual and ascetic life.

This book addresses specific problems of spiritual theology and the ascetic life.

It will later be read in Benedictine communities before a light meal, and from the Latin title, Collationes, comes the word collation in the sense of "light meal."

His third book, On the Incarnation of the Lord, is a defense of orthodox doctrine against the views of Nestorius, and is written at the request of the Archdeacon of Rome, later Pope Leo I.

His books, written in Latin, in a simple, direct style, are swiftly translated into Greek, for the use of Eastern monks, an unusual honor.

He dies in the year 435 in Marseille.

John Cassian's abbey and writings will influence St. Benedict, who will incorporate many of the same principles into his monastic rule (Rule of St. Benedict), and recommend to his own monks that they read the works of Cassian.

(Since Benedict's rule is still used by Benedictine, Cistercian, and Trappist monks, the thought of John Cassian still guides the spiritual lives of thousands of men and women in the Western Church.)