Under the control of the Visconti trade flourished and the city of Bellinzona grew.
 Even when an alternative route over the Alps, the  Schöllenen bridge opened, traffic in the St. Gotthard increased to the highest levels ever.
 During the second half of the 14th century a long wall, known as the Murata, was built across the entire valley of the Ticino, of which the bottom is about one kilometre wide at Bellinzona.
 This wall allowed Milan to protect and tax the trade route over the St. Gotthard Pass.
 While the city was controlled by Milan through the Visconti after 1340, the Visconti did not have a formal title and feudal rights until 1396 when they were granted by King Wenceslaus.
 However, the orderly growth of Bellinzona was threatened in 1402 when Duke Gian Galeazzo Visconti died.
 In 1403 Bellinzona was taken under the control of Alberto di Sacco of Val Mesolcina.
 He held Bellinzona until 1419 when it was taken over by Uri and Obwalden which had expanded into the Leventina Valley.
 Milan attacked the city three years later in 1422 after an offer to buy the city was rejected by the Swiss Confederation.
 The troops from Uri and Obwalden were quickly driven from the city and later defeated at the Battle of Arbedo on June 30, 1422.
 This defeat discouraged the expansionist intentions of Uri and its allies towards Lake Maggiore for a time.

During the period of unrest following Gian Galeazzo Visconti's death, a tower which would become the nucleus of the third castle, Sasso Corbaro, was built outside the city.

While the border between Uri and Milan was fixed in the peace treaty of 1426, in 1439 Uri invaded again.
 While they were unable to take Bellinzona, the victories of the Swiss troops led to Milan granting all of the Leventina Valley to Pollegio to Uri in 1441.
 Following the death of Duke Filippo Maria Visconti in 1447, Bellinzona was in the middle of the succession crisis between Franchino Rusca of Locarno and Heinrich of Val Mesolcina, who were allied with Uri and the Ambrosian Republic in Milan.
 The war following the succession crisis lasted nearly three years until Francesco I Sforza seized power in Milan.
 Bellinzona quickly accepted the new Sforza dynasty and the peace and stability that followed.

The peace was broken again in 1478 when the Swiss once again attacked Bellinzona unsuccessfully.
 However Swiss pride was restored by the Battle of Giornico which followed, where a force of 600 Swiss soldiers defeated 10,000 Milanese troops.
 Following the attack, Milan built Sasso Corbaro either on the site of a tower which had been built nearly a century before.
 The other two castles were strengthened and the Murata wall across the valley was rebuilt.
 Much of the modern castles and fortifications date from this period of construction in the late 15th century.
Under the control of the Visconti trade flourished and the city of Bellinzona grew.  Even when an alternative route over the Alps, the  Schöllenen bridge opened, traffic in the St. Gotthard increased to the highest levels ever.  During the second half of the 14th century a long wall, known as the Murata, was built across the entire valley of the Ticino, of which the bottom is about one kilometre wide at Bellinzona.  This wall allowed Milan to protect and tax the trade route over the St. Gotthard Pass.  While the city was controlled by Milan through the Visconti after 1340, the Visconti did not have a formal title and feudal rights until 1396 when they were granted by King Wenceslaus.  However, the orderly growth of Bellinzona was threatened in 1402 when Duke Gian Galeazzo Visconti died.  In 1403 Bellinzona was taken under the control of Alberto di Sacco of Val Mesolcina.  He held Bellinzona until 1419 when it was taken over by Uri and Obwalden which had expanded into the Leventina Valley.  Milan attacked the city three years later in 1422 after an offer to buy the city was rejected by the Swiss Confederation.  The troops from Uri and Obwalden were quickly driven from the city and later defeated at the Battle of Arbedo on June 30, 1422.  This defeat discouraged the expansionist intentions of Uri and its allies towards Lake Maggiore for a time.
During the period of unrest following Gian Galeazzo Visconti's death, a tower which would become the nucleus of the third castle, Sasso Corbaro, was built outside the city.
While the border between Uri and Milan was fixed in the peace treaty of 1426, in 1439 Uri invaded again.  While they were unable to take Bellinzona, the victories of the Swiss troops led to Milan granting all of the Leventina Valley to Pollegio to Uri in 1441.  Following the death of Duke Filippo Maria Visconti in 1447, Bellinzona was in the middle of the succession crisis between Franchino Rusca of Locarno and Heinrich of Val Mesolcina, who were allied with Uri and the Ambrosian Republic in Milan.  The war following the succession crisis lasted nearly three years until Francesco I Sforza seized power in Milan.  Bellinzona quickly accepted the new Sforza dynasty and the peace and stability that followed.
The peace was broken again in 1478 when the Swiss once again attacked Bellinzona unsuccessfully.  However Swiss pride was restored by the Battle of Giornico which followed, where a force of 600 Swiss soldiers defeated 10,000 Milanese troops.  Following the attack, Milan built Sasso Corbaro either on the site of a tower which had been built nearly a century before.  The other two castles were strengthened and the Murata wall across the valley was rebuilt.  Much of the modern castles and fortifications date from this period of construction in the late 15th century.
Castles of Bellinzona