During the long Investiture Controversy, an 11th-century dispute between Henry IV, Holy Roman Emperor and Pope Gregory VII over who would control appointments of church officials, Venice remained neutral, and this caused some attrition of support from the Popes. Doge Domenico Selvo intervened in the war between the Normans of Apulia and the Byzantine Emperor Alexios I Komnenos in favour of the latter, obtaining in exchange a bull declaring the Venetian supremacy in the Adriatic coast up to Durazzo, as well as "the exemption from taxes for his merchants in the whole Byzantine Empire", a considerable factor in the city-state's later accumulation of wealth and power serving as middlemen for the lucrative spice and silk trade that funnelled through the Levant and Egypt along the ancient Kingdom of Axum and Roman-Indian routes via the Red Sea.