Like many other mints, the Royal Mint issues bullion coins in precious metals, having much higher intrinsic value than their face value. The five ounce (5 oz) silver coins are denominated as ten pounds (£10).
The coins are legal tender but are not intended for circulation. They are targeted at bullion investors or collectors who appreciate the special editions as pieces of art. The coins are typically "one-year" types usually issued in parallel with smaller denominations with the same reverse designs.
Britannia as a symbol has been depicted on British coinage for centuries. The bullion series called Britannia has been issued in gold since 1987 and in silver since 1997; it has a "definitive" depiction as well as one-year designs like this one. The artist David Lawrence has decided to show her portrait in a classic design, wearing an ancient helmet.
The Royal Mint says:
"Britannia channels the spirit of a nation - a collective pride in our achievements and standing in the world. Instantly recognisable, Britannia is a true global icon - the personification of these ancient storied islands. For 2018 the design by David Lawrence, whose other designs include contributions to our five-year series commemorating the centenary of the First World War, assumes a more classical guise, a return to her Roman roots. Celebrate a significant milestone or mark a great moment for Britain with this exquisite coin." | 
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