00:00:12that you can hang the bridge from above
00:00:14but then of course that raises a whole
00:00:16new set of challenges how do you hang a
00:00:17bridge from above well you have to begin
00:00:21with towers Engineers use huge towers on
00:00:25either end of the bridge to suspend a
00:00:27flat roadway from
00:00:28arcing cables which are encased in 60000
00:00:31ton stone blocks called a garages on
00:00:33either Shore smaller cables called
00:00:36suspenders hang down from the main
00:00:39cables and hold up the roadway the heavy
00:00:41weight of the road pulls down on the
00:00:43cables but the Anchorage’s keep the
00:00:46cables pulled taut holding the road up
00:00:48the combined forces push down on the
00:00:51towers compressing them into a solid
00:00:53rigid mass
00:00:57since the towers cables and Anchorage’s
00:00:59do all the work of holding up the
00:01:01roadway additional pillars underneath
00:01:03aren’t needed keeping the river clear
00:01:06it’s an ingenious way to make a bridge
00:01:09and it also sort of seems to defy nature
00:01:11because there doesn’t seem to be any way
00:01:13that it’s being held up before now no
00:01:16one has dared used these engineering
00:01:18Marvel’s to cross a river this wide the
00:01:21Brooklyn bridges center span will need
00:01:22to be over 1500 feet 50 percent longer
00:01:26than any suspension bridge ever built
00:01:28connecting City Hall in Manhattan with
00:01:31downtown Brooklyn it seems like an
00:01:33impossible job but one man in America is
00:01:36up to the challenge a civil engineer
00:01:39named John Augustus Roebling even at one
00:01:43of the river’s narrowest points the
00:01:45bridge will require a center span that
00:01:47will stretch a staggering fifteen
00:01:48hundred ninety five and a half feet
00:01:52he will need 14,000 miles of wire to
00:01:55make the four main cables it hangs from
00:01:57to hold all that up he designs towers of
00:02:01stone taller than almost every building
00:02:04in the city but then tragedy strikes in
00:02:091869 while making final sightings for
00:02:12the bridge roebling’s foot is crushed by
00:02:14a ferry slamming into its slip his toes
00:02:18are amputated and he dies soon after of
00:02:22an infection
00:02:24one of the largest engineering projects
00:02:26ever attempted is internally
00:02:29but salvation is found close to home his
00:02:33son Washington Roebling must take his
00:02:36father’s place as chief engineer finally
00:02:40the massive effort is ready to begin on
00:02:42January 3rd 1870 the first of a
00:02:46workforce that would reach nearly 1,000
00:02:48men report to duty their first challenge
00:02:52is to erect the massive gothic arches
00:02:54that will one day become one of the
00:02:56bridges most iconic features but their
00:03:00foundations must rest on solid ground at
00:03:02river bottom to be sturdy
00:03:04that means Robley must somehow send men
00:03:07up to 80 feet underwater to dig away the
00:03:10riverbed down to bedrock Roebling turns
00:03:13to a risky new device an open bottom
00:03:17blocks of wood and iron called a caisson
00:03:20pneumatic caissons are basically large
00:03:24boxes that are placed upside down so
00:03:28that what would normally be the bottom
00:03:29of the boxes up at the top and the open
00:03:31bottom is facing down into the water
00:03:34sunk to the bottom of the river highly
00:03:36pressurized air is pumped into the open
00:03:38area forcing the water out men climb
00:03:42inside through airlocks to work in the
00:03:44craft pressurized space some compare it
00:03:48to hell unbearably hot and humid
00:03:51in danger from both fire and drought men
00:03:56spend a year toiling in these case odds
00:03:59digging away at a rate of more than a
00:04:01foot per day at the riverbed beneath
00:04:03them it was a challenge like no one had
00:04:06ever taken on before every day they
00:04:08would go down there through airlocks and
00:04:10gave with picks and shovels and slowly
00:04:13but surely go down through the riverbed
00:04:15down to bedrock
00:04:18but the pressurized air that keeps the
00:04:20water out also leads to a mysterious
00:04:23sickness
”