Progress on rebuilding Baltimore’s Francis Scott Key Bridge recently hit a new milestone as the Maryland Transportation Authority began the bridge’s Test Pile Program.

Six test piles, measuring 8 feet in diameter, over 220 feet high and made of American steel, were barged into the city. They vary in thickness from 1.5 inches to 2 inches and will be driven into the Patapsco River – after being vibrated into place – with a pile driving hammer.

A total of 12 test piles will be placed in the riverbed over the next 6 to 8 weeks and will require about 2 hours of hammering, which will sound similar to a large bell ringing in the distance, according to MDTA.