[2] In 1839, Clark moved back to Hungary to serve as resident engineer on the Chain Bridge, which was being built to link the twin towns of Buda and Pest across the Danube.

[3] The bridge's designer and chief engineer was an Englishman, William Tierney Clark (no relation), but he was unable or unwilling to remain in Hungary to supervise its construction.

[5] Clark in fact supported the revolutionaries, and in late 1848 assisted Lajos Kossuth's army in retreating across his bridge – still unfinished and untested.

In early 1849, he received information that the Austrian Imperial Army was planning to blow up the bridge, in order to prevent the rebels from crossing over from Pest to Buda.

He immediately took action to minimize any damage, flooding the bridge's anchorage chambers to ensure its stability and then destroying pumps.

He met with General Henryk Dembiński, the Hungarian commander-in-chief, and convinced him that it was not necessary to destroy the entire structure to make it impassable for troops.

[4] In 1850, Clark was commissioned by the Hungarian government to design and build a tunnel under Buda Castle, emerging directly opposite the Chain Bridge.

[10] Clark was deprecated somewhat by the Hungarian People's Republic during the 1950s, due to his association with the aristocracy, but his reputation was rehabilitated by later governments.