The Romans restored and expanded the system of the Illyrian hill-forts, and the top of the hill, on which the capitol rose, together with several public institutions and temples, had its own fortification system.
In the Middle Ages, the town walls were reinforced, and some of the Roman temples were turned into Christian churches.
In the 13th century a fortified town, Kastel, was built on top of the hill. The town walls were renovated in the 15th century, and in 1631 a new fortress (on the hill) was constructed.
From the second half of the 19th century a large number of utility (Arsenal) and representative buildings were built, predominantly in historic styles (the neo-classicist Admiralty, then the Officers' Casino, now the Centre of the Croatian Patriotic War Soldiers). Pula suffered heavy devastation during the Second World War.

The Roman Amphitheatre (commonly called Arena), from the 1st and 2nd centuries, occupies a dominant position above the harbour.
It has an elliptic ground-plan (132.45 x 105.10 m), the walls are 30.45 m high; it could seat 23,000 spectators. It is the world's sixth largest preserved amphitheatre.
The legend has it that it was built by Emperor Vespasian on the initiative of his Pula-born girl friend Cenida.
In the 15th century the Venetians transported several stone seats from the Amphitheatre's interior to use them as building material for their palaces.
The Ny-mp-h-a-eum leads to the southwest, with a way branching off to the Twin Gate (Porta gemina) from the 2nd century; an inscription is built-in above the Gate. The Twin Gate leads to the Archaeological Museum of Istria, with a park, in which exhibits are placed, in front of it.
The ruins of the Roman theatre, with preserved fragments of the orchestra and amphitheatrically arranged seats, are behind the Museum.
A part of the town wall running from the Twin Gate to the Hercules' Gate (Porta Herculea, from the mid-1st c. BC) has been preserved; the Gate is crowned by the bearded head of Hercules. The richly adorned Triumphal Arch of the Sergi, erected some time after 31 BC near the inner part of the main town gate (Porta aurea, collapsed in 1829), is reached from the Portarata Square.
A large Roman graveyard was located in front of the town gate, which Dante mentions in his Inferno (Canto IX); several marble sarcophaguses from the graveyard are housed at the Museo civico Correr in Venice.
Monte Zaro Park contains the ruins of the Roman theatre (Theatrum Juliae); the columns of the theatre were used in the construction of the St. Mark Library and the church of Santa Maria della Salute in Venice. Arsenalska Street leads from the park to the church of Our Lady of the Sea, built between 1891 and 1898.

Through the Triumphal Arch of the Sergi one enters Sergi Street, the busiest street in the old part of the town.
Clerisseau Street leads to the Dante Square, where a 15th-century Gothic church, reconstructed on several occasions, stands.
Flacius Street leads to the Byzantine memorial chapel from the 6th century, which was a part of the collapsed, grandiose basilica Santa Maria Formosa (Canneto), built around AD 556; the marble ornamentation and columns of the basilica were used in the construction of the San Marco Basilica in Venice.
In the interior of the chapel, the fragments of the 6th-century mosaics and mural paintings were preserved.
From Sergi Street down Matetic Ronjgov Street the way leads to the early mediaeval, now Christian Orthodox church of St. Nicholas, reconstructed in the 13th and 18th centuries; the wooden iconostasis with several Venetian icons dates back to the 16th and 17th centuries.
The street called Strmi Uspon sv. Franje Asiskog (Steep Ascent of St. Francis of Assisi) leads to the church of St. Francis from 1314, with a richly decorated Romanesque portal and octagonal Romanesque rose window; the church keeps an engraved polyptych from the end of the 14th century, made under the influence of the Vivarini School, one of the most valuable pieces of the Gothic wooden plastics in Istria.
A Gothic cloister with Renaissance adaptations is attached on the church; the cloister and the area in front of the church entrance accommodate stone collection of mediaeval monuments and a collection of copies of mural paintings from Istria.
Sergi Street terminates at Forum, which is located on the former Roman forum. The Temple of Augustus (of the goddess Romae and Emperor Augustus) from the 1st century is located on the northern side of the square, on an elevated base, with a portico comprising six Corinthian columns and a closed cella.
The Town Hall is near the temple, attached in 1296 to the Roman temple (of Diana); the back of the temple has been preserved.
The eastern façade of the Town Hall has rich late Romanesque ornamentation, and the façade facing the square, with a portico (loggia) on the ground-floor, was restored in 1653. Kandler Street, passing by the Town Hall, leads to the three-nave cathedral of St. Mary, built in the 5th century, restored in the 15th century and extended in 1640. The main front was built in the Renaissance style.
A Roman sarcophagus from the 3rd century is used as the main altar; the floor reveals fragments of the 5th and 6th-century mosaics. The Renaissance south portal was made in 1456.
The late Gothic Demartini palace (Kandler Street 12) is not far from the cathedral. From the cathedral a path leads to Kastel on the top of the hill.
Kastel has four protruding bastions built by the Venetians in 1631; under the Napoleon rule, Kastel was annexed, and restored in 1830. Today it houses the Historical Museum of Istria.

The Archaeological Museum of Istria was established in 1902. It contains the finds from the area of Istria, the islands of Cres and Losinj, dating from the antique and early mediaeval periods, as well as a collection of ancient and early mediaeval sculptures. The Museum comprises the following collections: one in the Temple of August (Roman busts), one in Arena (olive growing and viniculture) and the stone collection in the monastery of St. Francis. Kastel houses the Historical Museum of Istria, founded in 1955. It includes ten-odd collections of various exhibits (documents, photographs, photo-plates, graphics, records).