In 1092, Alexius I restored the currency which had been seriously affected by the debasement of gold and silver coinage in the 11th century. His reform introduced a slightly alloyed gold coin known as the hyperpyron (photo right) and its fractions: a 1/3 hyperpyron which contained one-third gold and two-thirds silver (which eventually degenerated to pure silver), and a 1/48 hyperpyron of base silver which in the end became indistinguishable from copper. These three denominations (called trachea by contemporaries) were concave rather than flat in shape and retained the weight of the gold nomisma introduced in the middle of the 11th century. At the lowest end of the monetary scale were small flat copper coins known as tetartera (see Case I, No. 21).