Background
In June 910, his father died and he became sole prince.
In June 910, his father died and he became sole prince.
In 909, he went to Constantinople to receive the titles of anthypatos and patrikios. He also continued a policy of alliance with Byzantium, but never servility. He never pledged to be a vassal of the emperor in Constantinople.
In 914, he succeeded in having the great abbey of Monte Cassino transferred from Teano to Capua and he and Atenulf appointed one John abbot.
The next year (915), they sent John as ambassador to Constantinople to renew the bonds of allegiance. The summer of 915, the forces of the new Byzantine strategos of Bari, Nicholas Picingli, joined those of various other south Italian princes: John I and Docibilis II of Gaeta, Gregory IV and John II of Naples, and Guaimar II of Salerno.
Together the Greco-Lombard army joined the northern forces of Pope John X and Alberic I of Spoleto and vanquished the Saracens at the Battle of Garigliano. According to Liudprand of Cremona, Landulf, a "potent prince", in answering a request for advice from the pope, initiated the alliance that brought an end to the Saracens on the Garigliano.
He downplays the coordinating role of John X in favour of that of Landulf, who is portrayed as militarily savvy.
In 921, he supported an anti-Greek Apulian rebellion, ravaging as far as Ascoli. In 923 or 926, by agreement with Guaimar, they would jointly attack Byzantine possessions, Landulf taking Apulia and Guaimar, Campania. Landulf was largely unsuccessful, though Guaimar was much southern
In 929, with Atenulf II, Guaimar II, and Theobald of Spoleto, he invaded Apulia and Calabria again.
This time, all were unsuccessful and Theobald hurt the old alliance. In 934, Guaimar was persuaded to quit the alliance by the Byzantine agent Cosmas of Thessalonica.
In 935, King Hugh of Italy gave his support to the Greeks. Within a few years, Landulf"s successful anti-Byzantine policy had been reversed and he was forced to make peace, but clashes continued: at Siponto in 936 and at Matera in 940.
He died four years later on April 10.