 At age 16 Mendelssohn wrote his String Octet in E @-@ flat major , the first work which showed the full power of his genius . This Octet and his Overture to Shakespeare 's A Midsummer Night 's Dream , which he wrote a year later in 1826 , are the best @-@ known of his early works . ( He later also wrote incidental music for the play , including the famous Wedding March , in 1842 ) . The Overture is perhaps the earliest example of a concert overture – that is , a piece not written deliberately to accompany a staged performance , but to evoke a literary theme in performance on a concert platform ; this was a genre which became a popular form in musical Romanticism . 
