4) Domes

• The largest dome in the world for more than 1700 years was the Pantheon in Rome. Its concrete dome spans an interior space of 43.45 m, which corresponds exactly to its height from floor to top. Its apex concludes with a 8.95 m wide oculus. The structure remained unsurpassed until 1881 and stills holds the title of the largest unreinforced solid concrete dome in the world. The Pantheon has exercised an immense influence on Western dome construction to this day.

• The largest dome out of clay hollowware ever constructed is the Caldarium of the Baths of Caracalla in Rome. The now ruined dome, completed in 216 AD, had an inner diameter of 35.08 m. For reduction of weight its shell was constructed of amphora joined together, a quite new method then which could do without time-consuming wooden centring.

• The largest half-domes were found in the Baths of Trajan in Rome, completed in 109 AD.

• The largest stone dome was the Western Thermae in Gerasa, Jordan, constructed around 150/175 AD. The 15m wide dome of the bath complex was also one of the earliest of its kind with a square ground plan.

5) Fortifications (Roman military engineering)

• The longest city walls were those of Classical Athens. Their extraordinary length was due to the construction of the famous Long Walls which played a key role in the city's maritime strategy, by providing it with a secure access to the sea and offering the population of Attica a retreat zone in case of foreign invasions. At the eve of the Peloponnesian War (431–404 BC), Thucydides gave the length of the entire circuit as follows: 43 stades (7.6 km) for the city walls without the southwestern section covered by others walls and 60 stades (10.6 km) for the circumference of the Peiraeus port. A corridor between these two was established by the northern Long Wall (40 stades or 7.1 km) and the Phaleric Wall (35 stades or 6.2 km). Assuming a value of 177.6 m for one Attic stade, the overall length of the walls of Athens thus measured about 31.6 km. The structure, consisting of sun-dried bricks built on a foundation of limestone blocks, was dismantled after Athens’ defeat in 404 BC, but rebuilt a decade later. Syracuse, Rome (Aurelian Walls) and Constantinople (Walls of Constantinople) were also protected by very long circuit walls.

6) Monoliths

• The largest monolith lifted by a single crane can be determined from the number of holes (each of which points at the use of one crane) in the lifted stone block. By dividing its weight by their number, one arrives at a maximum lifting capacity of 7.5 to 8 t as exemplified by a cornice block at the Trajan's Forum and the architrave blocks of the Temple of Jupiter at Baalbek. Based on a detailed Roman relief of a construction crane, the engineer O'Connor calculates a slightly less lifting capability, 6.2 t, for such type of a crane, on the assumption that it was powered by five men and using a three-pulley block.

• The largest monolith lifted by cranes was the 108 t heavy corner cornice block of the Jupiter temple at Baalbek, followed by an architrave block weighing 63 t, both of which were raised to a height of about 19 m. The capital block of Trajan's Column, with a weight of 53.3 t, was even lifted to 34 m above the ground. As such enormous loads far exceeded the lifting capability of any single treadwheel crane, it is assumed that Roman engineers set up a four-masted lifting tower in the midst of which the stone blocks were vertically raised by the means of capstans placed on the ground around it.

• The largest monoliths were two giant building blocks in the quarry of Baalbek: an unnamed rectangular block which was only recently discovered is measured at 20 m x 4.45 m x 4.5 m, yielding a weight of 1,242 t. The similarly shaped Stone of the Pregnant Woman nearby weights 1,000.12 t. Both blocks were intended for the Roman temple nearby, but were left for unknown reasons at their sites.

• The largest monolith was a group of three monumental blocks in the podium of the Jupiter temple at Baalbek. The individual stones are 19.60 m, 19.30 m and 19.10 m long respectively, with a depth of 3.65 m and a height of 4.34 m. Weighing approximately 800 t on average, they were transported to a distance of 800 m and probably pulled by the means of ropes and capstans into their final position. The supporting stone layer beneath features a number of blocks which are still in the order of 350 t. The various giant stones of Roman Baalbek rank high among the largest man-made monoliths in history.

• The largest monolithic columns were used by Roman builders who preferred them over the stacked drums typical of classical Greek architecture. The logistics and technology involved in the transport and erection of extra-large single-piece columns were demanding: As a rule of thumb, in the length range between 40 and 60 Roman feet (approximately 11.8 to 17.8 m), the weight of the column shafts, due to their larger diameter, doubled with every ten feet from 50 over 100 to 200 t. Despite this, forty and also fifty feet tall monolithic shafts can be found in a number of Roman buildings, but examples reaching sixty feet are only in evidence in two unfinished granite columns which still lie in the Roman quarry of Mons Claudianus, Egypt. One of the pair, which was discovered only in the 1930s, has an estimated weight of 207 t. All these dimensions, however, are surpassed by Pompey's Pillar, a free-standing victory column erected in Alexandria in 297 AD: measuring 20.46 m high with a diameter of 2.71 m at its base, the weight of its granite shaft has been put at 285 t.

• The largest monolithic dome crowned the early 6th century AD Mausoleum of Theodoric in Ravenna, then capital of the Ostrogothic kingdom. The weight of the single, 10.76 m wide roof slab has been calculated at 230 t.