The Post Office Tower aka. the BT Tower and the London Telecom Tower is 177 metres tall, with a further section of aerial rigging bringing the total height to 189 metres. The tower was designed by the architects of the Ministry of Public Building and Works. The narrow cylindrical shape was chosen because of the requirements of the communications aerials: the building will shift no more than 25 centimetres in wind speeds of up to 150 km/h.