The works executed by Telford under the Commissioners of Highland Roads and Bridges are of great importance. The practical operations under this commission, appointed in 1803, embraced about a thousand miles of new road, with nearly 1,200 new bridges, which caused the whole of Scotland, from its southern boundary near Carlisle, to the northern extremity of Caithness, and from Aberdeenshire on the east, to the Argyleshire islands on the west, to be intersected by roads; and its largest rivers and even inferior streams to be crossed by bridges. The execution of this undertaking occupied a period of twenty-five years, and all was done under the sole direction of Telford. The great road from London to Holyhead remains, perhaps, one of the most perfect specimens of his skill as an engineer; the improvements in it were executed by him, under another Parliamentary Commission appointed in 1815, and Telford himself appears to have regarded this work with peculiar satisfaction. The Menai suspension bridge is, however, unquestionably one of the noblest monuments of Mr. Telford's fame, and it may be said to have inaugurated the era of the extensive introduction of wrought iron into great permanent structures exposed to heavy strains.[39] This bridge was commenced in 1819, and opened for traffic in 1826. The distance between the two piers is 550 feet, and the whole roadway, which is carried over four arches on the one side, and three on the other, has a length of 1000 feet, and a breadth of 30 feet. The total cost of the work was 120,000_l._ Mr. Telford also built many other bridges of considerable size, and executed some important harbour works at Aberdeen and Dundee; but his most striking performance of this latter class is the St. Katharine Docks, London. One of his latest engagements was the survey of Dover harbour, undertaken in January, 1834, at the request of the Duke of Wellington, (as Warden of the Cinque Ports,) with a view to the adoption of measures to check the accumulation of shingle at the entrance. During the course of his life Mr. Telford taught himself Latin, French, and German, so as to be able to read those languages with fluency, and to be able to converse freely in French. He is likewise said to have been well acquainted with algebra, but to have placed more reliance upon experiment, than on mathematical investigation. He contributed to the 'Edinburgh Encyclopædia' the articles--'Architecture,' 'Bridge Building,' and 'Canal Making.' Besides the above, he wrote an account of his own life, giving elaborate descriptions of his various professional undertakings. (Life of Thomas Telford, written by himself. Edited by John Rickman. London, 1833, 4to.)