body was transported to Vilnius Cathedral, where she was finally buried on 23 June next to Elizabeth of Austria. Her death was a major blow to Sigismund; he often attended her coffin on foot while being transported to Vilnius in hot weather. Sigismund also became more serious and reserved; he avoided balls, temporarily renounced his mistresses and dressed black until death. The cause of Barbara's death is debatable. Her opponents and family members suggested sexually transmitted diseases due to a number of affairs she had before marrying Sigismund. There were also persistent rumors that she was poisoned by Queen Bona Sforza, who had a long history of eliminating her rivals or enemies quickly and efficiently. However, contemporary historians and experts agree on cervical or ovarian cancer. Third marriage The death of Queen Barbara Radziwiłł, five months after her coronation and under distressing circumstances, compelled Sigismund to contract a third, purely political union with his first cousin, the Austrian archduchess Catherine, to avoid an Austro-Russian alliance. She was also the sister of his first wife, Elizabeth, who had died within a year of her marriage to him, before his accession. Catherine, unlike previous queens, was considered dull and obese. Sigismund Augustus found her immensely unattractive despite accepting the marriage and organizing a pompous wedding ceremony on 30 July 1553. On the other hand, Catherine showed resentment towards Sigismund because of how he treated her sister and first wife, Queen Elizabeth. She accused him of negligence and indifference during her sudden illness, which caused premature death. The correspondence between the two remained purely formal and political for the remainder of their lives. Since her coronation, Catherine acted as Austria's puppet at the Polish court; she was tasked with espionage and obtaining important information for the benefit of the Habsburgs. Sigismund Augustus was aware of the scheme, but, by marrying Catherine, he obtained a promise from Austria to stay neutral and abandon plans with Russia. This neutrality was undermined by Catherine's actions, who followed her father's policy and objected the return of John Sigismund Zápolya and Isabella Jagiellon (Sigismund's sister) to Hungary. She would conspire with the Habsburg envoys prior to an audience with the king. She would also dictate what and how the envoys should express their views. When Sigismund Augustus found out of Catherine's intrigues, he sent her to Radom and excluded from political life. As Sigismund lost all hope of