The sackbut is a trombone from the Renaissance and Baroque eras and, along with the cornetto and organ, was one of the most important instruments in Baroque polychoral (a Venetian style of music which involved spatially separate choirs singing in alternation) works. It belongs to the brass family, a lot like a trumpet, except that it has a telescopic slide with which the player varies the length of the tube to change pitches.
Up until 1375, trumpets were just a long straight tube with a bell flare so the sackbut was the natural progression from this. More delicately constructed than their modern counterparts, and featuring a softer, more flexible sound, sackbuts attracted a larger repertoire of original chamber and vocal music than many other instruments at the time. It is thought that the name sackbut derives from the old French ‘sacqueboute’, which means ‘pull-push’.
There are a lot of words in the bible that sound like sackbut. This has led to a faulty translation from the Latin bible that suggested the trombones date back as far as 600 BC, but there’s no evidence of slides at this time.
1375 iconography sees trumpets being made with bends, and some in ‘S’ shapes.
Around 1400 the ‘loop’ shaped trumpet starts to appear in paintings and at some point in the 15th century, a single slide was added. However, the earliest evidence of a double slide instrument is in Filippino Lippi’s The Assumption of the Virgin, in Rome, which dates from 1488-1493.
From the 15th to the 19th centuries, the instrument designs changed very little overall, apart from a slight widening of the bell in the classical era, but since the 19th century, trombone bore sizes and bells have increased significantly.