History:
Mumbai is built on what was once an archipelago of seven islands: Bombay Island, Parel, Mazagaon, Mahim, Colaba, Worli, and Old Woman's Island (also known as Little Colaba).Pleistocene sediments found along the coastal areas around Kandivali in northern Mumbai by archaeologist Todd in 1939 suggest that these islands were inhabited since the Stone Age. It is not exactly known when these islands were first inhabited. Perhaps at the beginning of the Common era (2000 years ago), or even possibly earlier, they came to be occupied by the Koli fishing community. In the third century BCE, the islands formed part of the Maurya Empire, during its expansion in the south, ruled by the Buddhist emperor, Ashoka of Magadha. The Kanheri Caves in Borivali were excavated in the mid-third century BCE, and served as an important centre of Buddhism in Western India during ancient times. The city then was known as Heptanesia (Ancient Greek: A Cluster of Seven Islands) to the Greek geographer Ptolemy in 150 CE.
Between the second century BCE and ninth century CE, the islands came under the control of successive indigenous dynasties: Satavahanas, Western Kshatrapas, Abhiras, Vakatakas, Kalachuris, Konkan Mauryas, Chalukyas and Rashtrakutas, before being ruled by the Silhara dynasty from 810 to 1260.http://en.wikipedia.org/wiki/Mumbai - cite_note-31 Some of the oldest edifices in the city built during this period are, Jogeshwari Caves (between 520 to 525), Elephanta Caves (between the sixth to seventh century), Walkeshwar Temple (10th century), and Banganga Tank (12th century).King Bhimdev founded his kingdom in the region in the 12th or 13th century, and established his capital in Mahikawati (present day Mahim). The Pathare Prabhus, one of the earliest known settlers of the city, were brought to Mahikawati from Saurashtra in Gujarat by Bhimdev. The Muslim rulers of Gujarat annexed the islands in 1348. They were later governed by the Gujarat Sultanate from 1391 to 1534. The Sultanate's patronage led to the construction of many mosques, prominent being the Haji Ali Dargah in Worli, built in honour of the Muslim saint Haji Ali in 1431. From 1429 to 1431, the islands were a source of contention between the Gujarat Sultanate and the Bahamani Sultanate of Deccan. In 1493, Bahadur Khan Gilani of the Bahamani Sultanate attempted to conquer the islands, but was defeated.
The Mughal Empire, founded in 1526, was the dominant power in the Indian subcontinent during the mid-16th century. Growing apprehensive of the power of the Mughal emperor Humayun, Sultan Bahadur Shah of the Gujarat Sultanate was obliged to sign the Treaty of Bassein with Portuguese settlers on 23 December 1534. According to the treaty, the seven islands of Bombay, the nearby strategic town of Bassein and its dependencies were offered to the Portuguese. The territories were later surrendered on 25 October 1535. The Portuguese were actively involved in the foundation and growth of their Roman Catholic religious orders in Bombay. Some of the oldest Catholic churches in the city such as the St. Michael's Church at Mahim (1534), St. John the Baptist Church at Andheri (1579),St. Andrew's Church at Bandra (1580), and Gloria Church at Byculla (1632), date from the Portuguese era. On 11 May 1661, the marriage treaty of Charles II of England and Catherine of Braganza, daughter of King John IV of Portugal, placed the islands in possession of the British Empire, as part of Catherine's dowry to Charles. However, Salsette, Bassein, Mazagaon, Parel, Worli, Sion, Dharavi, and Wadala still remained under Portuguese possession. From 1665 to 1666, the British managed to acquire Mahim, Sion, Dharavi, and Wadala.

Geography:
Mumbai is located at 18°58′30″N 72°49′33″E / 18.9750°N 72.8258°E in the Indian state of Maharashtra. Mumbai consists of two distinct regions: Mumbai City district and Mumbai Suburban district, which form two separate revenue districts of Maharashtra. The city region is also commonly referred to as the Island City or South Mumbai. The total area of Mumbai is 603.4 km2 (233 sq mi), with the area of 437.71 km2 (169 sq mi), the island city spanning 67.79 km2 (26 sq mi) and the suburban district spanning 370 km2 (143 sq mi), coming under the administration of Brihanmumbai Municipal Corporation (BMC), while remaining area belongs to Defence, Mumbai Port Trust, Atomic Energy Commission and Borivali National Park, which are out of the jurisdiction of the BMC.
Mumbai lies at the mouth of the Ulhas River on the western coast of India, in the coastal region known as the Konkan. It sits on Salsette Island, partially shared with the Thane district. Mumbai is surrounded by the Arabian Sea to the west. Many parts of the city lie just above sea level, with elevations ranging from 10 m (33 ft) to 15 m (49 ft);  the city has an average elevation of 14 m (46 ft). Northern Mumbai (Salsette) is hilly, and the highest point in the city is 450 m (1,476 ft) at Salsette in the Powai-Kanheri ranges. Sanjay Gandhi National Park (Borivili National Park) is located partly in the Mumbai suburban district, and partly in the Thane district, and it extends over an area of 103.09 km2 (39.80 sq mi).