The Pópulo is the oldest quarter, the walled medieval town around the cathedral, with three surviving gates: the Arco de la Rosa, the Arco de los Blanco and the Arco del Pópulo. The name comes from a painting of the Virgin hung on one of the gates in the 16th century, with the words Ora pro populo, pray for the people.
Under the houses lies one of the biggest Roman theaters in Spain. It came to light in 1980 during excavations, and the interpretation center on Calle Mesón shows models and finds and lets you see the stage remains through shafts. The theater was built in the first century BC and abandoned in the third century AD, and later buildings, including a Muslim fortress, were stacked on top. The dig itself is closed during building works on the center, but the exhibition is free.
South of the Pópulo is the Barrio de Santa María, the southernmost of the old quarters, which grew in the 15th century as the town spilled beyond its walls. Its main square, Plaza de San Juan de Dios, has the town hall at one end. Santa María is the flamenco quarter. La Perla de Cádiz, on Calle Concepción Arenal, has shows on weekend evenings, usually Fridays (check its site), so it only fits if you stay for the weekend.