La cetra

La cetra (English: "The cetra"), Op. 9, is a set of 12 violin concertos. It was written by Antonio Vivaldi. It was written for Emperor Charles VI. The emperor gave him a medal and a lot of money for writing the concertos.
There is another set of 12 concertos called "La cetra". This set contains different concertos. It does not have an opus number. Its first violin parts are lost. It was not published.