Complex sentence: Large lamps were at the tops of the four towers, which were only to be lit when Queen Victoria was spending the night in London, and the central span was inscribed with the date of construction and the words "Gloria Deo in Excelsis".
Split into simpler sentences: Large lamps were set at the tops of the four towers, which were only to be lit when Queen Victoria was spending the night in London. The central span was inscribed with the date of construction and the words "Gloria Deo in Excelsis".