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principal contractors for mason work on the Caledonian Canal。
The building operations were begun with great vigour early in 1820。
The three arches on the Caernarvonshire side and the four on the
Anglesea side were first proceeded with。 They are of immense
magnitude； and occupied four years in construction； having been
finished late in the autumn of 1824。 These piers are 65 feet in
height from high…water line to the springing of the arches； the
span of each being 52 feet 6 inches。 The work of the main piers
also made satisfactory progress； and the masonry proceeded so
rapidly that stones could scarcely be got from the quarries in
sufficient quantity to keep the builders at work。 By the end of
June about three hundred men were employed。
The two principal piers； each 153 feet in height； upon which the
main chains of the bridge were to be suspended； were built with
great care and under rigorous inspection。 In these； as indeed in
most of the masonry of the bridge； Mr。 Telford adopted the same
practice which he had employed in his previous bridge structures；
that of leaving large void spaces； commencing above high water mark
and continuing them up perpendicularly nearly to the level of the
roadway。 〃I have elsewhere expressed my conviction；〃 he says； when
referring to the mode of constructing these piers； 〃that one of the
most important improvements which I have been able to introduce
into masonry consists in the preference of cross…walls to rubble；
in the structure of a pier； or any other edifice requiring strength。
Every stone and joint in such walls is open to inspection in the
progress of the work； and even afterwards； if necessary； but a
solid filling of rubble conceals itself； and may be little better
than a heap of rubbish confined by side walls。〃 The walls of these
main piers were built from within as well as from without all the
way up； and the inside was as carefully and closely cemented with
mortar as the external face。 Thus the whole pier was bound firmly
together； and the utmost strength given； while the weight of the
superstructure upon the lower parts of the work was reduced to its
minimum。
＇Image＇ Section of Main Pier
Over the main piers； the small arches intended for the roadways
were constructed； each being 15 feet to the springing of the arch；
and 9 feet wide。 Upon these arches the masonry was carried
upwards； in a tapering form； to a height of 53 feet above the
level of the road。 As these piers were to carry the immense weight
of the suspension chains； great pains were taken with their
construction； and all the stones； from top to bottom； were firmly
bound together with iron dowels to prevent the possibility of their
being separated or bulged by the immense pressure they had to
withstand。
The most important point in the execution of the details of the
bridge； where the engineer had no past experience to guide him； was
in the designing and fixing of the wrought iron work。 Mr。 Telford
had continued his experiments as to the tenacity of bar iron； until
he had obtained several hundred distinct tests； and at length；
after the most mature delilberation； the patterns and dimensions
were finally arranged by him； and the contract for the manufacture
of the whole was let to Mr。 Hazeldean； of Shrewsbury； in the year
1820。 The iron was to be of the best Shropshire； drawn at Upton
forge； and finished and proved at the works； under the inspection
of a person appointed by the engineer。
＇Image＇ Cut showing fixing of the chains in the rock
The mode by which the land ends of these enormous suspension chains
were rooted to the solid ground on either side of the Strait； was
remarkably ingenious and effective。 Three oblique tunnels were made
by blasting the rock on the Anglesea side； they were each about six
feet in diameter； the excavations being carried down an inclined
plane to the depth of about twenty yards。 A considerable width of
rock lay between each tunnel； but at the bottom they were all
united by a connecting horizontal avenue or cavern； sufficiently
capacious to enable the workmen to fix the strong iron frames；
composed principally of thick flat cast iron plates； which were
engrafted deeply into the rock； and strongly bound together by the
iron work passing along the horizontal avenue； so that； if the iron
held； the chains could only yield by tearing up the whole mass of
solid rock under which they were thus firmly bound。
A similar method of anchoring the main chains was adopted on the
Caernarvonshire side。 A thick bank of earth had there to be cut
through； and a solid mass of masonry built in its place； the rock
being situated at a greater distance from the main pier； involving
a greater length of suspending chain； and a disproportion in the
catenary or chord line on that side of the bridge。 The excavation
and masonry thereby rendered necessary proved a work of vast
labour； and its execution occupied a considerable time； but by the
beginning of the year 1825 the suspension pyramids； the land piers
and arches； and the rock tunnels； had all been completed； and the
main chains were firmly secured in them； the work being
sufficiently advanced to enable the suspending of the chains to be
proceeded with。 This was by far the most difficult and anxious part
of the undertaking。
With the same careful forethought and provision for every
contingency which had distinguished the engineer's procedure in the
course of the work； he had made frequent experiments to ascertain
the actual power which would be required to raise the main chains
to their proper curvature。 A valley lay convenient for the purpose；
a little to the west of the bridge on the Anglesea side。
Fifty…seven of the intended vertical suspending rods； each nearly
ten feet long and an inch square； having been fastened together； a
piece of chain was attached to one end to make the chord line 570
feet in length； and experiments having been made and comparisons
drawn； Mr。 Telford ascertained that the absolute weight of one of
the main chains of the bridge between the points of suspension was
23 1/2 tons； requiring a strain of 39 1/2 tons to raise it to its
proper curvature。 On this calculation the necessary apparatus
required for the hoisting was prepared。 The mode of action finally
determined on for lifting the main chains； and fixing them into
their places； was to build the central portion of each upon a raft
450 feet long and 6 feet wide； then to float it to the site of the
bridge； and lift it into its place by capstans and proper tackle。
At length all was ready for hoisting the first great chain； and
about the middle of April； 1825； Mr。 Telford left London for Bangor
to superintend the operations。 An immense assemblage collected to
witness the sight； greater in number than any that had been
collected in the same place since the men of Anglesea； in their
war…paint； rushing down to the beach； had shrie