By regnal year 23 — the last full year before Antoninus Pius died in March 161 — the Alexandrian mint was producing billon tetradrachms with a silver fineness that had been declining steadily for decades. These late issues of his reign tend to surface in better condition than mid-reign pieces, not from any minting improvement but simply because production volumes in the final years were lower and hoarding appears to have followed his death closely.
By regnal year 23 — the last full year before Antoninus Pius died in March 161 — the Alexandrian mint was producing billon tetradrachms with a silver fineness that had been declining steadily for decades. These late issues of his reign tend to surface in better condition than mid-reign pieces, not from any minting improvement but simply because production volumes in the final years were lower and hoarding appears to have followed his death closely.