King Edward I (1272–1307) successfully introduced the halfpenny as part of his new coinage, which allowed trade to increase. As with all coins of this period, the denomination was not written on the coin, which was worth its weight in silver; thus a halfpenny was half the size and weight of a penny. All hammered halfpennies tend to be difficult to identify because they are small, often clipped, and in poor condition, and the legends on the coins are often incorrect because of the difficulty in making dies which were small enough for the denomination. The fact that Kings Edward II, III, and IV also issued halfpennies makes it difficult to distinguish between them – in general, Edward I's coins are slightly larger than his successors'. As with other denominations, by far the majority of coins were produced at the London mint, in the Tower of London, but five other mints were active in Edward I's reign. The legend on the reverse of the coin identifies the mint's name, and reads CIVITAS LONDON or LONDONIENSIS for London, VILLA BRISTOLLIE for Bristol, CIVITAS LINCOL for Lincoln, NOVI CASTRI for Newcastle upon Tyne, CIVITAS EBORACI for York, and VILLA BEREVVICI for Berwick-upon-Tweed.