| Type | Offensive alliance |
|---|---|
| Signed | 27 May 1657 |
| Location | Vienna, Archduchy of Austria |
| Signatories | |
| Parties |
The Treaty of Vienna, concluded on 27 May 1657, was an Austro–Polish alliance during the Second Northern War.[1]
After Habsburg emperor Ferdinand III had agreed to enter the war on the anti-Swedish side and support the Polish king John II Casimir with 4,000 troops in the ineffective Treaty of Vienna (1656), his death in April 1657 made way for a more substantial treaty with his successor Leopold I.[1] By this treaty, Leopold I promised to aid John II Casimir with 12,000 troops against the Swedish-Brandenburgian alliance.[1] These troops were to be maintained at Polish expense, and crossed the Polish border in June.[1]