A collection of nine CryptoPunk non-fungible tokens (NFTs) sold for $16.9 million at auction house Christie’s on Tuesday.

CryptoPunks are a collection of 10,000 pixelated heads. They come in the form of humans, apes, zombies and aliens.

The nine separate and rare NFTs were sold by Larva Labs, the creator of CryptoPunks itself, from its own collection. Christie’s hasn’t yet disclosed the buyer.

While Christie’s said the sale made history, it appears to be dissatisfying. Earlier this year, a single alien CryptoPunk was sold for $7.6 million.

This was Christie’s second NFT sale. The auction house sold a Beeple NFT for $69 million in March. Its third NFT sale by American model Emily Ratajkowski will go up for auction on Friday.

NFT activity has been on the decline over the past few weeks. According to The Block’s Data Dashboard, weekly NFT trading volumes have dropped significantly from their peak in February. Weekly users and transactions of NFT platforms have also declined.