In A Golden Thread — 2500 years of solar architecture and technology, solar architectures in ancient Greece and Rome are described (Butti and Perlin 1979). According to Perlin »Probably more significant developments in solar technology have occurred on Italian soil than anywhere else in the world."

Almost 2500 years ago, the ancient Greeks began designing their cities and homes taking into consideration the microclimate, in particular the sun, the winter winds and summer breezes. Olynthus and Priene are among the most important examples of ancient Greek solar urban planning. Greek principles were later to be found in Roman architecture. Vitruvio, a Roman architect who lived in the 1st century B. C., in his famous On Architecture wrote: "Buildings are correctly sited if region and latitude features have been taken adequately into account. In fact buildings should be built in one way in Egypt, in another way in Spain, still differently in Rome, and so on in all other areas having different features either of the land or of the Sun, whose influence on Earth depends on the distance from it which can be close, far or in between… therefore buildings must be oriented according to the different features of regions and climates."

Interest in solar architecture in ancient Rome was also fuelled by energy crisis, due to shortages and high prices of burning wood. Wood and charcoal were common fuels for Rome’s Baths and Villas, where space and water central heating systems, called hypocausts, were installed.

Heated air from hypocausts by burning wood in furnaces (praefurnia) flowed under floors and through walls by means of terracotta “tubuli”.

Heated floors and walls irradiated their warmth to the surrounding indoor spaces. In the Baths, water used in the caldarium, the warmest room of the Baths, was heated in large bronze boilers called "tartarughe della vasca" integrated into appropriately placed furnaces.

The installations described above can be seen at many Roman archaeological sites, where also Vitruvio’s precepts of

The remains of Pompeii, Herculaneum and the great baths in Rome and other cities of the Empire provide evidence of the important developments produced by the Romans in solar energy. From the first century A. D. on, under Augustus, and until Rome’s fall, the advances achieved by the Romans in the use of solar energy seem to have been put to fairly wide use throughout the Empire, though only among the wealthy classes.

The Romans had learned to make glass (very low quality compared to the today’s transparent glass) and to use the greenhouse effect to heat their homes, baths and greenhouses. Transparent surfaces were probably made also with translucent stones, like mica and alabaster, to trap solar heat, which was stored under the floors or in the walls with high thermal capacity.

For the first time in history, the Roman Empire enacted laws regulating “sun-rights” and similar matters.

In the first century A. D., for instance, the emperor Diocletian issued an edict setting prices for window glass (six or eight denarii per pound, depending on its quality).

Romans created a special room called heliocaminus heated by the sun’s radiation passing through south facing glass panes. The heliocaminus was the origin of legal actions on "sun — rights" due to its need for sunlight. Ulpiano, a lawyer of the II century A. D., claimed that the heliocaminus "sun-rights" must be protected. These rights were introduced four centuries later in Justiniano’s codes.

Rome for the first time issued a law to protect "sun-rights" and enforced urban planning and architecture principles aimed at promoting the exploitation of solar light and heat.

Therefore the archaeological remains of Rome, sometimes still standing nearly as they were two thousand years ago, are places where reflections on many aspects of the history of solar architecture and technology as well as of the history of energy use and civilizations are spontaneous, easily accompanied by strong emotions and feelings.