Which Byzantine coin replaced the Solidus as the empire's standard gold coinage in the late eleventh century?

Under Alexios I, significant monetary reforms were implemented to address the declining quality of the Byzantine currency. In 1092, he discontinued the debased solidus (tetarteron and histamenon) and introduced a higher-quality gold coinage known as the hyperpyron. This new coin had a fineness of approximately .900-.950 and weighed 4.45 grams, though it was slightly smaller than its predecessor. Alongside the hyperpyron, he introduced two additional coins: the electrum aspron trachy, worth one-third of a hyperpyron and consisting of about 25% gold and 75% silver, and the billon aspron trachy (or stamenon), valued at 48 to the hyperpyron with a 7% silver wash. Copper coins, the tetarteron and noummion, were worth 18 and 36 of the billon aspron trachy, respectively.

The most ancient of all of the Heraldic symbols dating to the time of the crusades is the 'bezant' or gold coin. The term Bezant is of Eastern origin being derived from the name Byzantium, the gold roundel representing a Byzantine coin.