Odysseus, Pericles, Thucydides - these names will be dropped, somewhere, by every modern guidebook worth its salt which attempts to introduce you to the archaic and classical past of Greece. Another name will often crop up, usually unexplained, in its descriptions of ancient sites. It is less familiar, but worth noticing: Pausanias.

Pausanias lived in the second century AD and wrote the earliest guide to Greece that has survived. He provides us with our most complete picture of what the ancient Greek world would have looked like, and has been plundered by travel guides ever since.

His was a grand plan: to describe the experience of visiting all of Greece, or at least those places and things in Greece he deemed impor tant. He was aiming at the educated tourist (a growth industry at the time), particularly the élite from his native Asia Minor who could be expected to make their own Grand Tour. He would also have hoped to inform the armchair tourist back at home, or even in Rome.

Because the Greeks could teach the Romans a thing or two about the past, Pausanias's account, though revealing aspects of Greece's life under Roman rule, is in fact far more interested in the past. He guides us round Greece with an eye to antique objects: he has a noticeable preference for the sculpture and painting of the fifth century BC, and rather loses interest after 150BC. (You wouldn't know from his account of the Acropolis, for instance, of certain statues and temples erected by Roman emperors which must have been prominent at the time he was writing.)

He describes ancient statues, pictures, tombs and sanctuaries, digressing at length on their legends, history and religious traditions. From these, he seems to be saying, stems the Greek identity. There is more than a touch of 'ya boo' to the Romans - you might have conquered the land, but the Greek past will ever be present.

Yet for all the details he provides for this burgeoning tourist market, Pausanias was probably not widely read in antiquity (and particularly not on site: imagine all those scrolls_) So why the fuss?

Largely because, being the sole complete survivor of the 'ancient guidebook' tradition, he has proved invaluable to excavation work. His information helped early archaeologists to locate ancient sites which had been neglected or silted over. It then helped them to work out what to look for, and to imagine what the remains represented. He comes in particularly useful on statues. A base often remains without its statue, but reconstuction books can have a field day using Pausanias's descriptions to re-draw what they might have looked like. The current reconstruction work at Epi davros and Delphi is helped not least by our Pausanias.

All in all, a service to the modern traveller - because, let's face it, when you get to the Glory of Greece, you can often miss the glory for what appears to be simply a pile of old stones. A friend of mine, who teaches classics, once asked a group of teenagers to write down as many adjectives as they could to describe the statue of Athene. They came up with 'broken', 'old' and 'statue' (a tribute to their imagination and their grammar). If you too arrive on site and feel dismayed at what seems like a mess of broken old statues, turn to Pausanias.

• Pausanias's Guide to Greece is available in two volumes from Penguin Classics, £10.99 each.