The Tamar was a formidable obstacle to overcome. Brunel chose a point three miles north-west of Plymouth, where the river narrows, to make the crossing but even so, it is 1000ft wide and 70 ft deep at high water here.

A design consisting of two 455ft main spans was settled upon, with a central deep water pier. Seventeen approach spans were required, varying from 69ft to 93ft wide.

The main spans consist of two trusses, the top members of which are tubular wrought iron parabolic arches. They support 72 ft long wrought iron girders carrying the train track. The girders are supported by 20ft suspension chains, one hung from each side of the arches.

Many of the suspension chains used here were originally made for the Clifton Suspension Bridge, the construction of which had been held up owing to financial difficulties (it was completed after Brunel's death).

The trusses and chains are supported by three towers that rise 50ft above track level. The two side towers are built of masonry. Arches above track level form portals for the trains.

The central tower is made of cast iron sections and masonry. It was founded on bedrock 96ft below high water level using a compressed air technique developed by John D'Urban Hughes in the early 1850s and refined by Brunel's assistant, R.P. Brereton.

In all, the foundation works for the bridge took 3 years to complete.

Brunel survived the completion of the bridge by only four months. The directors of the railway company had his name set over each portal as a memorial.

Renewals and detail modifications have been made to the bridge at various times since 1928 to enable it to carry heavier trains and to counter corrosion-fatigue. Brunel's bridge is still the only semi-suspension bridge in daily use on a main trunk railway.

Contractor: C.J. Mare