If you arrived in Rome between the 15th and 19th centuries, you entered through the Porta del Popolo at the north end of this piazza. The Via Flaminia from the north — from Florence, from France, from everywhere that wasn't Rome — ended HERE. The first thing you saw: an Egyptian obelisk (1200 BC, Ramesses II, brought from Heliopolis by Augustus in 10 BC) flanked by two SEEMINGLY identical churches — Santa Maria dei Miracoli and Santa Maria in Montesanto. They look like twins. They are not. The right church is WIDER (its plot was wider) so the architect (Carlo Rainaldi, finished by Bernini) adjusted the dome shape — one is circular, one is oval — so they APPEAR identical from the piazza. Architecture as optical illusion. Rome as theater.
The obelisk (Flaminio, 1200 BC): The second-oldest obelisk in Rome (after the Lateran). Ramesses II. Brought from Heliopolis by Augustus. This stone was ancient when Rome was FOUNDED. Santa Maria del Popolo (north side of piazza): The church you must NOT miss. Inside: 2 Caravaggio paintings (Conversion of St. Paul + Crucifixion of St. Peter, Cerasi Chapel, 1601 — look at Paul FALLEN from the horse, the light hitting his face as God intervenes, the horse taking up most of the composition because the ANIMAL doesn't know what's happening). Raphael's Chigi Chapel (designed by Raphael, mosaics by him, finished by Bernini 120 years later). Pinturicchio frescoes (first chapel right). All free.
The Pincio terrace: Walk up from the piazza's east side to the Pincio gardens — the BEST viewpoint over the piazza, over Rome, over the dome of St. Peter's at sunset. The three streets (il Tridente): From the piazza, three streets radiate south: Via del Babuino (toward Piazza di Spagna), Via del Corso (straight to Piazza Venezia — Rome's main shopping street), Via di Ripetta (toward the Tiber). The Tridente system was designed so that a traveler entering Rome through the gate could choose their direction — pilgrimage, commerce, or river.
Metro A: Flaminio. Free piazza, always open. Santa Maria del Popolo: free, open 7:30-12:30 + 16-19. The Caravaggio paintings require no ticket and no queue — walk in, turn right, last chapel. Most visitors don't know they're there. Day 3 or Day 7 →