Coin collecting is big business and the rarest, most coveted specimens fetch unbelievable prices when they come on the market. From precious ancient Greek coins to the modern million-dollar Canadian gold sovereign that is as big as a coffee table, check out the 30 most valuable coins ever.

Only three of these medieval gold florins are known to exist, and two of them reside at the British Library in London. Dating from the reign of King Edward III, the rare coins are worth hundreds of thousands of dollars each – in 2006, this specimen sold to a private collector for $566,000 (£460k).

The most valuable British coin sold at auction, this extremely rare trial gold sovereign was minted just before King Edward VIII's abdication in December 1936 and never made it into circulation. It was auctioned for $635,000 (£156k) in 2014.

This exquisite silver coin from Crete depicts Herakles, the divine hero with superhuman strength, and dates from 350BC. One of the most sought-after coins from the ancient world, it sold for 16 times its pre-sale estimate in 2012.

The Silver Tetradrachm, which features the wine god Dionysus and his drunken tutor Silenus, is considered one of the finest coins of the fifth century BC – it went for a cool $850,000 (£691k) at auction in 2012.

This extremely rare proof $5 coin – only one of two in existence – is unique thanks to its overstamped date. Part of the legendary D. Brent Pogue Collection, it exceeded its reserve price and fetched $940,000 (£765k) at auction in New York earlier this year.

Another exquisite rare coin from the D. Brent Pogue Collection, this 1795 Draped Bust $1 is in exceptionally good condition and has been described as the finest example of its kind. It was sold along with rest of the collection in May.

This gold yuan beauty was minted in 1992, and forms part of a limited edition of 10. The coveted 2000 yuan coin, which weighs a kilo and depicts a compass as well as the Great Wall of China, realised $1,298,000 (£1m) at auction in Hong Kong in 2011.

The vast majority of $5 Capped Head Half Eagle coins were melted following the Mint Act of 1834. As a result, very few survive today. This example from the D. Brent Pogue Collection sold for $1,351,000 (£1.1m) in May 2016.

The stunning 8-Aurei Gold Medallion is the most expensive Roman coin sold at auction, and then some. One of only two surviving examples, it is notable for its generous size, fine detailing and exceptional quality.

The most expensive Chinese coin ever, the 10,000 yuan Gold Panda coin, which was struck in 1991, weights an impressive five kilos and is made from .999 fine gold. It garnered $1,567,190 (£1.3m) at auction in 2011.

One of the first coins ever produced by the US Mint, this silver-centre cent is one of just six in existence. Needless to say, the historically important coin fetched a fortune at an auction in Chicago in 2014, and another example fetched $705,000 (£574k) earlier in the year.

The most valuable and finest of the famous 1894-S Barber Dimes, this particular example sold for just shy of $2,000,000 (£1.63m) in 2016. Only 24 1894-S Barber Dimes were struck. Of those 24, just 10 survive.

Very few gold 1907 $10 Rolled Edge Eagles still exist, and collectors have entered into fierce bidding wars to get hold of these elusive coins. Unsurprisingly, the best example sold for $2,185,000 (£1.8m) at auction in 2011.

One of just 15 specimens that are known to exist, this Class III example of the 1804 Bust, aka the Bowed Liberty Dollar, went for a very respectable $2,300,000 (£1.9m) when it was auctioned in 2011.

The very first penny struck by the US mint, this collector's dream coin is likely to have been handled by George Washington and Thomas Jefferson. As you'd expect, it realised an astronomical price at auction last year.

Goldsmith Ephraim Brasher produced the first American gold coins, only seven of which survive. Of those that have been preserved, this version, which features the EB punch on the eagle's breast, is one of the most valuable. It fetched $2,990,000 (£2.4m) at auction in 2005.

Regarded as the most beautiful of all the American coins, the rare $20 gold Double Eagle was designed by Beaux-Arts architect Augustus Saint-Gaudens. This 1907 example sold for almost $3,000,000 (£2.44m) in 2005.

This stunning gold stater depicts the face of a satyr on the head and a griffin on the reverse. It realised $3,802,500 (£3.1m) when it was sold in 2012, a record price for an ancient Greek coin.

Meticulously crafted, this Ivan VI Silver Rouble from 1704 is only one of two or three specimens known to exist. It fetched $3,858,850 (£3.13m) at auction in 2012, which is a world record for a Russian coin.

South Africa's rarest gold coin, the 1898 Single 9 Pond is a unique error coin featuring an oversized '9' stamp on the head side. Much sought-after, the fabled coin was sold to a private collector for a colossal $4,000,000 (£3.3m) in 2010.

The size of a coffee table, this 2007 Canadian gold coin weighs a hefty 100 kilos and has a face value of C$1,000,000 (£607k). It was bought by a consortium of international buyers for $4,000,000 (£3.3m) at an auction in Austria earlier this year.

The finest examples of the 1804 Bust Dollar are Class I pieces and as such they command the highest prices. This specimen sold for $4,140,000 (£3.4m) in 1999, while another fetched $3,877,500 (£3.2m) at auction in 2013.

Another of Ephraim Brasher's exquisite gold doubloons, this impeccable early specimen, which features the EB punch on the eagle's wing, was sold for $4,582,500 (£3.7m) at a Florida auction in 2014.

The prized Flowing Hair Dollar was the first dollar coin issued by the US federal government and is now the most coveted by collectors. This perfectly preserved specimen from the Lord St. Oswald Collection went for $4,993,750 (£4.1m) at auction last year.

Only five 1913 nickels exist bearing the Liberty Head design. Heritage Auctions sold one for $3,737,500 (£3m) in 2010 and another for $3,172,500 (£2.6m) in 2013. The most valuable example, the so-called Eliasberg Specimen, was bought by a private collector for $5,000,000 (£4.1m) in 2007.

This super-rare $10 gold coin dated 1804 was specially minted in 1834 for President Andrew Jackson to give as a diplomatic gift to officials in Asia. Only four of them exist. This particular specimen garnered $5,000,000 (£4.1m) at a 2007 auction.

Regarded as the rarest and most important Islamic gold coin, the Umayyad Gold Dinar is historically significant and highly prized. It went for $6,029,400 (£4.9m) at auction in 2011, beating its $400,000 (£325k) reserve by a long shot.

The very first doubloon minted by Ephraim Brasher, which was stamped with EB on the eagle's breast, remains the most expensive historic coin ever sold. It was bought by a Wall Street investment company for $7,400,000 (£6m) in 2011.

All but two of the mythical 1933 $20 Saint-Gaudens Double Eagles were ordered to be melted down, but around 13 are known to exist. Exceedingly valuable, the only specimen to come on the open market sold for a staggering $7,590,020 (£6.2m) in 2002.

The world's most valuable coin, this 1794 Flowing Hair Dollar is the finest known example and was among the first dollar coins minted. Dubbed 'a national treasure' by numismatic expert Steven Contursi, it realised a phenomenal $10,016,875 (£8.1m) at auction in 2013.