Main gateway to the Castrum Sancti Donati, the one from which the Via Marsicana was accessed. The Arco di San Donato, at the beginning of the development of the castrum, connected the urban and rural worlds, allowing entry to those coming from Abruzzo or those returning from work in the fields. Through the Via Pedicata below, the gate connected to the contrada Sbarra, a probable block for those who wanted to access the castle.

In the anonymous Report of 1595 the urban core is described as "populous" and has "air buonissima, et sottile." The inhabitants are "armiggeri, industriosi et fatiganti, vanno attorno fatigando, fanno de li panni di lana per loro uso et per vendere. There are de le cacciie di lepri, et capri, pernici et quaglie assai, et le gente si dilettano de la caccia."

The pointed arch structure of the Arch of San Donato is after the 1349 earthquake, when the Cantelmo family, having inherited the fief from the Counts of Aquino, renovated it in the French style. Inside, the stone hinges that supported the doors are visible.

The area outside the arch is called "Ammarieglie" in dialect, in memory of the Gambarelli family, which in the 11th century arrived in San Donato Castle from Sant'Urbano, a vanished town once located between Alvito and San Donato. From this location, on July 29 each year, the patron saint appears to give a blessing to the town. The Porta a Levante is ideal for taking panoramic photographs of the historic center and the Comino Valley.

At this place, the patron saint faces to give a blessing to the village, and it is an ideal place to take panoramic photographs of the medieval village.