Casascius coins, one of the first physical representations of bitcoin were released for sale

On September 6, 2011, one of the first physical representation of bitcoins were released for sale on the Bitcoin Talk Forum. These coins, created by Bitcoin enthusiast Mike Caldwell, were designed to represent digital Bitcoin value in a tangible form.
 

The Casascius coins were unique because they contained an actual piece of paper inside them with a Bitcoin private key, which was covered by a tamper-resistant hologram. The coins themselves were made of brass and were available in various denominations, including 1, 10, 25, 100, and 1000 BTC increments.
 

The idea behind these coins was to make Bitcoin, a purely digital asset, more accessible and understandable to the general public by giving it a physical form. This also allowed for face-to-face transactions using Bitcoin in a way that was similar to traditional money. The first person to redeem the private key could claim the Bitcoin value, after which the coin would no longer hold any Bitcoin value.