See Puerta de Alcalá#22 of 27 things to do in Madrid
You should approach it close enough and then you will see the inscription right over the central arch "Rege Carolo III. Anno MDCCLXXVIII" ("King Charles III, 1778"). It has been placed here in honour of King Charles III, who has built the gate.
On the side arches you will see the statues of four virtues - wisdom, justice, temperance and courage.
Where to do?
Combining baroque and neoclassicism, the gate in the Independence Square in Madrid has been one of the most beautiful sights of the city for a long time.4Madrid