nction of the two rivers is the
place for defending both of these valleys, and has consequently, in all
ages of the world, been a very important post. The Romans built a town
here, in the days of Julius Caesar, and the town has continued to the
present day. It is called Coblenz. The Romans named it originally
_Confluentes_, which means the _confluence_; and this name, in the
course of ages, has gradually become changed to Coblenz.

Coblenz is built on a three-cornered piece of flat land, exactly on the
point where the two rivers come together. There is a bridge over the
mouth of the Moselle where it comes into the Rhine, and another over the
Rhine itself. The bridge over the Moselle is of stone, and was built a
great many hundred years ago. That over the Rhine is what is called a
bridge of boats.

A row of large and solid boats is anchored in the river, side by side,
with their heads up the stream, and then the bridge is made by a
platform which extends across from boat to boat, across the whole
breadth of the stream.

Near the Coblenz side of the bridge there are two or three lengths of it
which can be taken out when necessary, in order to let the steamers, or
rafts, or tow boats, that may be coming up or down the river, pass
through. Rollo was very much interested, while he remained at Coblenz,
in looking out from the windows of his hotel, which faced the river, and
seeing them open this bridge, to let the steamers and vessels pass
through. A length of the bridge, consisting sometimes of _two_ boats
with the platform over it, and sometimes of _three_, would separate from
the others, and float down the stream until it cleared itself from the
rest of the bridge, and then would move by some mysterious means to one
side, and so make an opening. Then, when the steamer, or whatever else
it was, had passed through, the detached portion of the bridge would
come back again slowly and carefully to its place.

Of course all the travel on the bridge would be interrupted during this
operation; but as soon as the connection was again restored, the streams
of people would immediately begin to move again over the bridge, as
before.

Across the bridge, on the heights upon the other side, Rollo could see
the great Castle of Ehrenbreitstein, together with an innumerable
multitude of walls, parapets, bastions, towers, battlements, and other
constructions pertaining to such a work.

One day Mr. George and Rollo went over to see thi