Fortification was well understood, as may still be seen in the remains of walled and escarped strongholds on hills and in steep ravines, while lagoon-cities like Mexico had the water approaches defended by fleets of boats and the causeways protected by towers and ditches; even after the town was entered, the pyramid-temples with their surrounding walls were forts capable of stubborn resistance.
The city stands on an island of the same name, which forms one of a group now connected by causeways with the mainland.
During a reign of twelve years (1002-1014) he is said to have effected much improvement in the country by the erection and repair of churches and schools, and the construction of bridges, causeways, roads and fortresses.
Whole forests, vast quarries of granite, and hills of gravel were used in fringing the water margins, constructing wharves, piers and causeways, redeeming flats, and furnishing piling and solid foundations for buildings.
Around the peninsula are spanned by causeways and bridges, East Boston only, that the harbours may be open to the navyyard at Charlestown, being reached by ferry (1870), and by the electric subway under the harbour.
About the middle of the 15th century their mud-and-rush dwellings were partly replaced by stone structures, grouped around the central enclosure of the great teocalli, and bordering the causeways leading to the mainland.