One must disengage them from this thick covering, and excavate the soil, often to a great depth.  Assyrian palaces may be reached only by cutting into the hills.  A trench of forty feet is necessary to penetrate to the tombs of the kings of Mycenae.  Time is not the only agency for covering these ruins; men have aided it.  When the ancients wished to build, they did not, as we do, take the trouble to level off the space, nor to clear the site.  Instead of removing the debris, they heaped it together and built above it.  The new edifice in turn fell into ruins and its debris was added to that of more remote time; thus there were formed several strata of remains.  When Schliemann excavated the site of Troy, he had passed through five beds of debris; these were five ruined villages one above another, the oldest at a depth of fifty feet.

By accident one town has been preserved to us in its entirety.  In 79 A.D. the volcano of Vesuvius belched forth a torrent of liquid lava and a rain of ashes, and two Roman cities were suddenly buried, Herculaneum by lava, and Pompeii by ashes; the lava burnt the objects it touched, while the ashes enveloped them, preserving them from the air and keeping them intact.  As we remove the ashes, Pompeii reappears to us just as it was eighteen centuries ago.  One still sees the wheel-ruts in the pavement, the designs traced on the walls with charcoal; in the houses, the pictures, the utensils, the furniture, even the bread, the nuts, and olives, and here and there the skeleton of an inhabitant surprised by the catastrophe.  Monuments teach us much about the ancient peoples.  The science of monuments is called Archaeology.

=Inscriptions.=—­By inscriptions one means all writings other than books.  Inscriptions are for the most part cut in stone, but some are on plates of bronze.  At Pompeii they have been found traced on the walls in colors or with charcoal.  Some have the character of commemorative inscriptions just as these are now attached to our statues and edifices; thus in the monument of Ancyra the emperor Augustus publishes the story of his life.

The greatest number of inscriptions are epitaphs graven on tombs.  Certain others fill the function of our placards, containing, as they do, a law or a regulation that was to be made public.  The science of inscriptions is called Epigraphy.

=Languages.=—­The languages also which ancient peoples spoke throw light on their history.  Comparing the words of two different languages, we perceive that the two have a common origin—­an evidence that the peoples who spoke them were descended from the same stock.  The science of languages is called Linguistics.

=Lacunae.=—­It is not to be supposed that books, monuments, inscriptions, and languages are sufficient to give complete knowledge of the history of antiquity.  They present many details which we could well afford to lose, but often what we care most to know escapes us.  Scholars continue to dig and to decipher; each year new discoveries of inscriptions and monuments are made; but there remain still many gaps in our knowledge and probably some of these will always exist.