From The Opera Companion, by George Martin (John Murray, 1961), pp. 133-134:
In Italy in the eighteenth century the center of operatic activity shifted from Venice to Naples, where a school of outstanding composers arose specializing in two styles: “opera seria” and “opera buffa.” “Opera seria” was on a grand scale with historical or mythological themes; it was a close cousin to the Viennese Baroque opera except that the music was of greater importance and the scenery of less. The aria, generally sung by a castrato, was the crux of every scene, and over the years it became extremely stylized, so that for any situation there was a certain type of aria that was appropriate. The singer was expected to embellish the aria with extemporaneous runs, trills and flourishes, and this—more than the drama, scenery or composed music—was what excited the audience. Thus the composer wrote a vehicle for a particular singer rather than searching his soul in nineteenth-century romantic style to produce an immortal masterpiece. Grout, in A Short History of Opera, reports that forty leading composers in the eighteenth century wrote fifty operas each: Verdi wrote twenty six, Wagner thirteen, and Puccini twelve. There was no repertory as today. The audience wanted new music each year, although it was perfectly willing to have the same librettos used over and over; for example, Mozart’s was the seventh setting of Metastasio’s La Clemenza di Tito. The scores of the operas were almost never published and, in any event, were extremely sketchy. Only the favorite arias might be published and, as there was no copyright, the composer was far less interested in preserving his old work for posterity than in receiving a commission for a new one, which he could complete in four to six weeks.
One result of this approach to opera, so different from today’s, was that no one really listened much; opera was still a social rather than a musical event. A Frenchman, De Brosses, writing in 1740 described what went on at Rome: “The ladies hold, as it were, at homes in their boxes, where those spectators who are of their acquaintance come to call on them. I have told you that everyone must rent a box. As they are playing at four theatres this winter, we have combined to hire four boxes, at a price of twenty sequins each for the four; and once there I can make myself perfectly at home. We quiz the house to pick out our acquaintance, and if we will, we exchange visits. The taste they have here for the play and for music is demonstrated far more by their presence than by the attention they pay. Once the first scenes are past, during which the silence is but relative, even in the pit, it becomes ill-bred to listen save in the most interesting passages. The principal boxes are handsomely furnished and lighted with chandeliers. Sometimes there is play, more often talk, seated in a complete circle as is their custom, and not as in France, where the ladies add to the show by placing themselves in a row in the front of each box; so you will see that in spite of the splendour of the house and the decoration of each box, the total effect is much less fine than with us.”
Besides visiting in the opera, the Romans also played cards and chess. In Milan the diversion was faro. Florence offered hot suppers served in the boxes. At Turin each box had a room off it with a fireplace and all the conveniences for refreshments and cards. At Venice the boxes could be closed off from the theater by a shutter.
All travelers reported that the gabble and noise were deafening except during two or three favorite arias which, greeted with wild applause, were repeated. One visitor, Lalande, estimated that the typical Milanese spent a quarter of his life at the opera. It is not surprising then that the archduke’s box in Milan had attached to it not only a private sitting room but also a bedroom.