Short answers, pulled from the story.
The Roman road network comprised more than 400,000 kilometers of roads at its peak, of which over 80,500 kilometers were stone-paved. The empire's 113 provinces were interconnected by 372 great roads, with 29 major military highways radiating from Rome itself.
The miliarium aureum, or golden milestone, was a gilded bronze monument erected by Augustus in 20 BC near the Temple of Saturn in Rome. It listed all the major cities of the empire and the distances to each, and was considered the symbolic starting point of all roads in the empire. Constantine later called it the umbilicus Romae, the navel of Rome.
Roman road builders excavated a trench called the fossa down to bedrock, then filled it with rubble and gravel in successive layers. Near the surface they added a tamped gravel layer called the pavimentum, which could be topped with a stone foundation (statumen), coarse concrete (rudus), fine concrete (nucleus), and a final course of polygonal paving stones called the summa crusta, crowned at the center for drainage.
Ulpian divided Roman roads into viae publicae, the state-funded main highways named after the censors who built them; viae privatae, privately constructed country roads that could be dedicated to public use; and viae vicinales, the local roads running through villages and crossroads, maintained by local canton magistrates.
Horse-drawn carts could cover 40 to 50 kilometers per day on Roman roads, while pedestrians averaged 20 to 25 kilometers per day. The official postal relay service, the cursus publicus, could carry a letter approximately 80 kilometers in a single day using horse relays. Tiberius covered 296 kilometers in 24 hours using the mutationes changing stations as chariot relays.
Julius Caesar and Mark Antony commissioned the first known master road itinerary in 44 BC. Three Greek geographers, Zenodoxus, Theodotus, and Polyclitus, were hired to survey the entire road system and compile it, a task that required more than 25 years. The completed stone-engraved itinerary was installed near the Pantheon in Rome.