velarium

noun

1. The marginal membrane of certain medusae belonging to the Discophora.
2. (historical)An awning that stretched over the seating area of the Colosseum in Ancient Rome and other Roman amphitheaters.
3. A cloth stretched over another space, such as that stretched below the roof of the Royal Albert Hall.

   “In accordance with the epochal significance of the occasion, Berlin was decked out as never before in its history. […] A velarium suspended over Unter den Linden depicted the great military victories that had finally brought Germany its unity.”

   “Royal Albert Hall [was dedicated] by the Prince of Wales (later King Edward VII). As The Times reported on the next day: 'The address [...] was somewhat marred by an echo [...]'. To Col. Scott, the designer of the huge roof structure, this acoustic problem was a mere irritant which could be solved by a velarium of cloth (weighing 1+¹⁄₄ tons) stretched underneath the roof. But in spite of experiments with the height of the velarium, the echo persisted […]”