The Rock of Gibraltar is not native rock at all in the geological sense of belonging here: its Jurassic limestone was shoved north from Africa some five million years ago, when tectonic pressure folded the Betic and Rif ranges together and left a 426-metre monolith stranded at the mouth of the Mediterranean. The promontory has been contested ever since people learned to sail past it. Phoenician sailors left votive offerings in its sea caves. The Moorish commander Tariq ibn Ziyad landed in 711 and gave the place its name — Jabal Tariq, Tariq's mountain, worn down by centuries of tongues into Gibraltar. The Moorish Castle's Tower of Homage still stands above the town, its walls pocked by shot from fourteen recorded sieges. Spain ceded the territory to Britain under the Treaty of Utrecht in 1713. The Great Siege of 1779 to 1783 produced the Great Siege Tunnels, hand-cut galleries driven through solid limestone by military engineers working with sledgehammers and gunpowder. Later wars extended those workings to more than fifty kilometres of tunnel, a network longer than the territory's public road system. What draws travellers on a malaga to gibraltar day trip by bus today is the compression of it all. Within the Upper Rock Nature Reserve sit St. Michael's Cave, a chamber of stalactites used as an emergency hospital in the Second World War and now a concert auditorium; the Windsor Suspension Bridge, strung across a seventy-metre gorge; and the Barbary macaques, Europe's only free-living monkey population, descended from animals brought from North Africa in the eighteenth century. The Skywalk platform stands 340 metres above sea level. On clear days the Rif Mountains of Morocco are visible across fourteen kilometres of strait. The territory itself measures 6.7 square kilometres and houses roughly 32,000 people, who speak English, Spanish and the code-switching hybrid called Llanito. Its airport runway crosses Winston Churchill Avenue, so road traffic halts for landings. British pillar boxes stand beside Genoese shutters and Andalusian tilework — an architectural record of Genoese merchants, Sephardic and Moroccan traders, Portuguese labourers and Maltese settlers who arrived through the naval dockyard. The Upper Rock Nature Reserve, at Gibraltar Nature Reserve, Upper Rock, Gibraltar, opens 09:00–18:15 daily and carries a conservation fee of 20 GBP per person. Guided Gibraltar coach tour from Malaga services and independent malaga to gibraltar day trip by bus tickets both deliver visitors to the same frontier, roughly 130 kilometres down the Costa del Sol from the Málaga coast.