Among London's many problems as it grew at the beginning of the nineteenth century was travel between the two banks of the river Thames, which held important ports that could accept shipping coming up the river from the channel. Bridges would interfere with that important trade, so in the years of the 19th century engineers began to examine the only other option: instead of going over, going under the river.
The Reconquista, or Christian reconquest of Iberia, took nearly 800 years. The fighting did not come without great attempts by Muslim powers across the strait trying to reestablish their presence in mainland Europe. The last gasp of that effort came in the 1330s, when the powerful Marinid sultanate of what is modern Morocco invaded in an attempt to reverse Christian gains and secure the perilous position of the Sultanate of Granada.