This week is one of my favorite old colorized photo post cards.  I was fortunate to purchase it recently.  A lone chunk of wall starts a series of sections to that would eventually be Gatun Locks   Large forms are used to create the massive walls and culverts. The large vertical form sections were made of steel and mounted on tracks in order that they could be moved after each section  was poured.  Each section took about a week to complete.  Overhead cables brought large buckets of concrete and dumped into the form sections.  It never ceases to amaze me as I study the methods used by these great engineers 100+ years ago.