building. The basic steps in brick making
are the same today as they were
thousands of years ago. First, workers
dig up the clay. Sometimes they mix the
clay with sand or other materials to
make it stronger. Next, workers form the
clay into small, rectangular blocks called
bricks. After the bricks dry, workers
bake, or fire, them in very hot ovens
called kilns.
Builders use bricks mainly to make
walls, but floors and walkways can also
be made of bricks. To make strong walls,
builders lay the bricks in interlocking
patterns. This means that each brick lies
on more than one other brick. Builders
People attend a church in Brazzaville. Most
of the people in the Republic of the Congo
practice some form of Christianity.
128 Brazzaville BRITANNICA STUDENT ENCYCLOPEDIA
fill in the spaces between the bricks with
mortar, or sand mixed with cement and
water.
Tile
Like brick, tile is also made from baked
clay. However, tiles are thinner than
bricks. They may also be curved or cut
into geometric shapes. In addition, there
are more kinds of tile than of brick. Tiles
made of red clay, called terra-cotta tiles,
have surfaces that are easy to mold. This
type of tile has long been used for covering
roofs.
When tiles are coated with glaze and
then fired at high temperatures, they are
called ceramic tiles. The glaze gives them
a shiny, colorful appearance and makes
them waterproof. Ceramic tiles cover the
walls and floors of many kitchens and
bathrooms.
Today some tiles are made from plastic
and other artificial materials. Artificial
tiles cover walls and floors in many
modern buildings.
History
The ancient Babylonians made brick
houses 6,000 years ago. The ancient
Egyptians, Greeks, and Romans also
built with bricks and tiles. The Romans
were especially good at making tiles.
They even used tiles to build pipes that
carried water. Native Americans in dry
regions built houses with adobe, or sundried,
bricks.
Early builders often made their bricks
right at the construction site. In the
1800s people developed new and faster
ways of making bricks and tiles. Factories
began producing them in large
quantities. Today many builders use
newer construction materials such as
concrete and cinder blocks. Nevertheless,
brick and tile are still popular building
materials. They are also commonly
used in drainage systems.
#More to explore
Adobe • Clay • Sand
Blue and white tiles decorate
steps in Portugal.
Bricks are laid in an interlocking pattern in
order to build a strong wall.
BRITANNICA STUDENT ENCYCLOPEDIA Brick and Tile 129
Bridge
A bridge is a structure that allows
people and vehicles to cross over an
open space. Bridges span, or stretch
across, deep pits in the earth, bodies of
water, and roads.
Types of Bridges
The beam bridge is the oldest, simplest,
and most common type of bridge. A
beam bridge is a horizontal, or level,
structure. It has a support on each end.
Other supports, called piers, may also
hold up the bridge between the two
ends. A log or a plank that crosses a
stream is a beam bridge in its most basic
form. Modern beam bridges are usually
made of steel beams, called girders. Most
highway bridges are beam bridges.
Like the beam bridge, the truss bridge
has a support at each end. It may also rest
on piers in between. But a truss bridge is
stronger than a simple beam bridge. A
framework of metal or wood bars
connects the two ends of the bridge.
These bars fit together in triangular
shapes. They often form a sort of tunnel
through which the roadway passes.
The cantilever bridge is made up of
structures called cantilevers. A cantilever
is a beam that has a pier at only one end,
like a diving board. A framework of
many bars adds strength to the beam, as
in a truss bridge. At least two of these
beams stretch toward each other to form
a cantilever bridge.
Like the beam bridge, the arch bridge is
a very old design. An arched structure
built beneath the bridge’s roadway provides
its support. Arch bridges often
span rivers and valleys.
In the suspension bridge, the roadway
hangs from strong wires called cables.
The main cables hang between two or
more towers. Smaller cables hang down
from the main cables. The smaller cables
hold up the roadway. Suspension bridges
can span longer distances than any other
type of modern bridge.
A cable-stayed bridge also uses cables to
support the roadway. Its cables run
There are six basic bridge forms. They are
the beam, the truss, the cantilever, the arch,
the suspension, and the cable-stayed.
130 Bridge BRITANNICA STUDENT ENCYCLOPEDIA
directly between the towers and the
roadway. They attach to the roadway in
straight, diagonal lines.
Some types of bridges are movable.
Some may open upward to allow tall
ships to pass underneath. Others may
turn sideways. Still others, called pontoons,
float on water.
History
Early humans built bridges from logs,
branches, or stones. They also made
suspension bridges with long, tough
vines. The ancient Romans built many
stone arch bridges that still exist today.
Modern bridge building began in the
1700s. People began building bridges
from iron and, later, steel. These metals
