The Puerta de Sevilla is the main gate into Carmona's old town, and it is an impressive thing: a double-arched Roman gateway built into a substantial Almohad fortress, the whole ensemble rising high above the road that approaches from the plain. What looks like a single gate is actually a barbican — attackers who forced the outer arch found themselves in an enclosed killing ground before they could reach the inner gate.
Inside the gate, the tourist office offers guided tours of the interior of the fortress, which includes a rooftop terrace with good views over the lower town and the Corbones plain below. The Almohad additions date from the 12th century and include some well-preserved decorative brickwork. Worth the modest entry fee to get above the roofline.