Some 600,000 gold bars, worth nearly $300 billion, are stashed around London. For good measure, there are also a million silver bars in London vaults, adding another $19 billion to the city’s precious metal holdings.

Until recently, no one knew exactly how much gold and silver were stored in the vaults of the British capital. But this week, in the name of “transparency,” the London Bullion Market Association (LBMA) published this data for the first time.

London is a major gold-trading center. In March, the city was clearing, on average, $18.1 billion (pdf) in gold each day. In comparison, the average daily turnover on the Shanghai gold exchange is around $1 billion.

The Bank of England holds most of the gold and silver in London—over 60% of the total share—and already publishes details of its holdings. What’s interesting in the new LBMA data, then, is that we now know how much private custodians—HSBC, JP Morgan, and ICBC Standard Bank among them—keep in their vaults.

For central banks, maintaining gold reserves is a legacy from the time when it was mandated, and typically an inflation hedge or service offered to private companies. For this reason, it’s not surprising that the Bank of England oversees around 400,000 bars of gold, or that the Federal Reserve Bank of New York stores close to 540,000. (The Bank of England itself only owns two bars of gold, so the rest of the metal in its vaults belongs to the British treasury, other central banks, commercial lenders, and other firms.)

But private institutions’s gold holdings are a different story, and these numbers are worth watching. If their holdings fluctuate, it can indicate a lack of confidence or rise in anxiety about the economy. We can now track this more accurately, since the LMBA plans on publishing stats each month.