The view you may admire if you look up entering the great hall of the Villa Borghese Pinciana in Rome. I will not speculate on its size, but the fresco is for sure more than 100 meter big.
Frescoes was a very popular technique used to decorate ceilings and walls in Rome, in ancient times as well as during the Renaissance. It was adopted in many other places and countries usually in churches, palaces and villas belonging to the rich. The technique was also applied in China and India. The true fresco technique involves painting with a water colour on the wet plaster. If the painter did not manage to put colour onto the plaster before it dried up, the plaster had to be removed and put on once again. Frescoes were also painted with a technique called fresco secco, where the painting was applied on a dry plaster. (Secco stands in Italian for dry, fresco – for fresh). The major difference between a true fresco and the fresco secco is its durability. In case of a true fresco during the drying process the colour becomes part of the plastered wall and this way the fresco painting may preserve longer. True frescoes are not suitable as a painting technique for countries where the climate is wet and cold.