example, ridges extending from Dalry and Ardmillan, and also Sighthill. Craigmillar Castle is also on top of a small hill, and there is another small one underneath Colinton. There are also hills beneath the New Town, and the Old Town to the south of the Cowgate. Some of these hills rise to heights substantially above the traditional seven — for example parts of Fairmilehead at . The Pentland Hills to the south of Edinburgh are traditionally thought of as being outside the city, although they are very close, and because of their height they dominate views to the south of the city. Allermuir Hill at 493m is only slightly further from the centre of Edinburgh than Corstorphine Hill, and is almost twice the height of Arthur's Seat. A number of Edinburgh suburbs, also contain "hill" or synonyms in their name — Abbeyhill, Alnwickhill, Church Hill, Curriehill, Drylaw (Lowland Scots for a "hill without a spring"), Ferniehill, Firrhill, Greenhill, Piershill, Sighthill; and others also contain the element "Craig" meaning a large rock, such as Craigentinny and Craigmillar. Hills in the centre of the city Edinburgh is also traditionally thought of as being a hilly city, because of the number of hills in or close to the city centre. Chief among these is the Royal Mile which rises continuously from Holyrood House to Edinburgh Castle for approximately a mile. Others include - Dundas Street and Hanover Street, which rise steeply from the Water of Leith to a summit at George Street, then descend slightly to Princes Street, before climbing the very steep Mound to join the Royal Mile Several streets in the New Town which run parallel to Dundas Street and Hanover Street for part of their length, including Frederick Street and Castle Street Leith Walk, which rises continuously from just above sea level at Leith, to a summit at Princes Street. A number of short and very steep streets in the Old Town, including Victoria Street, Candlemaker Row, and Infirmary Street. The many height changes have led to several roads crossing other roads on bridges, which was relatively rare in pre-20th century Britain. These include Waterloo Place above Calton Road, George IV Bridge over the Cowgate and Merchant Street, South Bridge over the Cowgate, and King's Bridge carrying Johnston Terrace over Kings Stables Road. There are also several staircases accessible to pedestrians only, linking streets at different heights, including Playfair Steps