Border disputes involving the ill-defined Swiss-Italian frontier increase with the number of traders and mercenaries crossing the St. Gotthard Pass.

The Swiss Confederation is attempting to expand into the southern foothills of the Alps to gain control of both ends of the valuable mountain passes.

In November 1478, Uri troops move south over the Gotthard pass into the Levantina valley.

The population of the valley, who have long been opposed to Milan, greet the Swiss troops as liberators and allies.

However, below the valley at Bellinzona, they find the city gates closed.

Uri is quickly joined by forces from other Confederation cantons and establishes a siege camp below the walls of Bellinzona on November 30, 1478.

Ludovico Sforza, acting as regent to the young Duke of Milan, Gian Galeazzo Sforza, responds by sending ten thousand men toward Bellinzona to drive the Confederates back and reassert his control over the Val Levantina.

The Milanese army reaches Magadino on Lake Maggiore, about fourteen kilometers (8.7 miles) from Bellinzona, on December 16.

However, the Confederates have already retired, after a fourteen-day siege of Bellinzona, to the Gotthard Pass.

Only a one hundred and seventy-five man-strong reserve army, reinforced by about four hundred soldiers from the Val Levantina, are guarding the rear at Giornico in the Levantina valley.

The entire Milanese army reaches Giornico on December 28, outnumbering the defenders by about twenty to one.

The Milanese army is confined in a narrow valley, struggling for foothold on the December snow and ice.

The Swiss ambush the army from above, creating confusion by rolling large boulders down the hillside.

They reportedly also wore crampons for better foothold.

Against this attack, the Milanese army is helpless regardless of their superior number, and are forced to flee, leaving an estimated fourteen hundred dead.

Following this decisive defeat,Ludovico Sforza withdraws from the Levantina, leaving it under Uri's control.

To consolidate his power in Bellinzona, Sforza builds the small Sasso Corbaro castle near the town of Bellinzona.

Ludovico Sforza, known as "Il Moro" because of his swarthy complexion, was born on July 27, 1452, at Vigevano, in what is now Lombardy.

He is the second son of Francesco I Sforza and Bianca Maria Visconti and, as such, had not been expected to become ruler of Milan.

Nevertheless, his mother, Bianca, had prudently seen to it that his education was not restricted to the classical languages.

Under the tutelage of the humanist Francesco Filelfo, Ludovico had received instruction in the beauties of painting, sculpture, and letters, but had also been taught the methods of government and warfare.

He had later helped Leonardo da Vinci paint with pastels.

When their father Francesco died in 1466 (the Last Supper was painted next to his burial place in Santa Maria delle Grazie), the family titles had devolved upon the dissolute Galeazzo Maria, the elder brother, while Ludovico had received the courtesy title of Count of Mortara.

Galeazzo Maria had ruled until his assassination in 1476, leaving his titles to his seven-year-old son, Gian Galeazzo Sforza, Ludovico's nephew.

A bitter struggle for the regency with the boy's mother, Bona of Savoy, had ensued; Ludovico emerges as victor in 1481 and seizes control of the government of Milan, despite attempts to keep him out of power.

For the following thirteen years he will rule Milan as its regent, having previously been created Duke of Bari in 1479.