<br>Construction plan of the aqueduc crossing the Trepsenbach by <a href="https://en.wikipedia.org/wiki/Robert_Maillart" class="extiw" title="en:Robert Maillart">Robert Maillart</a> for the power station Wägital, 1923; Schwyz, Switzerland.
Robert Maillart (scanned, reworked and uploaded by <a href="//commons.wikimedia.org/wiki/User:Chriusha" title="User:Chriusha">Хрюша</a>, 2011-07-13)
1923
<i>Das Kraftwerk Wägital</i>.  Schweizerische Bauzeitung (e-lib.ch), Heft 24 von 1931, Seite 306.