Early cannons had only a limited range and were unreliable; in addition early stone cannonballs were relatively ineffective when fired at stone castle walls. As a result, early cannon proved most useful for defence, particularly against infantry assaults or to fire at the crews of enemy trebuchets. Indeed, early cannons could be quite dangerous to their own soldiers; James II of Scotland was killed besieging Roxburgh Castle in 1460 when one of his cannons, called "Lion", exploded next to him. The expense of early cannons meant that they were primarily a weapon deployed by royalty rather than the nobility.