Banking Law and Financial Network Topology Risk in Spain

Introduction

Financial network topology risk refers to the danger that the structure of connections among banks, financial institutions, markets, governments, companies and non-bank financial institutions can transmit or amplify financial stress. A bank may appear financially sound when examined individually, yet still create or face systemic risk because of its position within a wider financial network.

In Spain, this subject forms part of banking supervision, systemic-risk regulation, macroprudential policy and bank-resolution law. The Banco de España has specifically developed maps of the Spanish financial system to understand interconnectedness and possible channels through which financial stress can spread. Its analysis identifies banks as playing a pivotal role in Spain's financial network and considers connections among banks, investment funds, insurers, pension funds, companies, households, government and foreign financial markets.

Network topology risk is therefore not a separate statutory category called "network topology law." Rather, it is addressed through the broader Spanish and EU rules governing capital, liquidity, concentration risk, systemic institutions, large exposures, stress testing, recovery and resolution, and macroprudential supervision.

Legal and Regulatory Framework

Spanish banking regulation operates within the EU Banking Union. Important national legislation includes Law 10/2014 on the regulation, supervision and solvency of credit institutions, together with EU capital-requirement legislation and the Single Supervisory and Single Resolution Mechanisms.

The Banco de España's macroprudential mandate is particularly relevant. It explains that systemic risk may develop when financial imbalances accumulate and that macroprudential instruments are intended both to prevent such risks from building and to provide buffers capable of absorbing their consequences. Its available instruments include the countercyclical capital buffer, buffers applicable to systemically important institutions, sectoral measures and concentration-related tools.

The regulatory objective is therefore broader than preventing the insolvency of one institution. Authorities must consider whether difficulties at one institution could spread through the network and interfere with credit provision, payment systems, financial markets or the wider economy.

Understanding Network Topology Risk

A financial network can be imagined as a collection of nodes and links.

The nodes include banks, investment firms, insurers, investment funds, central counterparties, companies and public institutions. Links may represent loans, deposits, derivatives, securities holdings, guarantees, payment obligations or other financial exposures.

Several characteristics are particularly important.

Centrality risk arises where one institution has an unusually important position in the network. Its failure can affect numerous counterparties.

Concentration risk exists where many institutions depend on the same counterparty, market, asset class or funding source.

Contagion risk means losses or liquidity difficulties at one institution spread to others.

Common-exposure risk can occur even without direct bank-to-bank connections. Several banks holding similar assets may suffer simultaneously when those assets decline sharply.

Cross-border risk arises because Spanish institutions have connections with financial institutions and markets outside Spain.

Banco de España research using granular Spanish interbank data has demonstrated how financial distress may propagate through a credit-quality channel and how the impact can depend on banks' balance-sheet characteristics, including leverage.

Interbank Network Risk

Direct lending between banks is one of the clearest examples of network topology.

If Bank A has a significant exposure to Bank B and Bank B suffers severe losses, Bank A can suffer losses as well. If Bank A consequently becomes distressed, its creditors may then experience losses. The original shock can therefore travel through several layers of the network.

The Banco de España's Spring 2025 Financial Stability Report recorded increased participation by major Spanish banks in the interbank market between December 2021 and December 2024. Funding granted through that market increased by 40.9%, while funding obtained increased by 60.2% over that period. The report also identified stronger connections with foreign banks, particularly French and German institutions.

These figures do not mean that interconnectedness automatically produces instability. Connections can distribute liquidity and risk efficiently. The regulatory concern is whether the structure, size and concentration of those connections could amplify a severe shock.

Macroprudential Supervision and Stress Testing

Traditional banking supervision examines the safety of individual banks. Network-risk analysis adds a system-wide perspective.

Authorities therefore use stress testing to examine how adverse developments could affect the financial system as a whole. Banco de España's systemic analytical framework incorporates empirical and theoretical models covering endogenous risks, macro-financial imbalances and external shocks.

The Banco de España also regularly performs macroprudential stress tests to assess the banking system's aggregate capacity to absorb economic and financial shocks.

The objective is to identify circumstances in which individually manageable losses become systemically significant because institutions are connected.

Bank Resolution and Network Risk

Resolution law is particularly important when network risk actually materialises.

Under the EU Single Resolution Mechanism, authorities may intervene where the statutory requirements for resolution of a failing or likely-to-fail bank are satisfied. Resolution seeks, among other objectives, to preserve critical functions and limit significant adverse consequences for financial stability.

The 2017 resolution of Banco Popular Español generated extensive EU litigation and provides the strongest Spanish-related body of case law for understanding the legal consequences of systemic banking distress.

It should be stressed that the following cases are not judicial decisions establishing a separate doctrine called "network topology risk." Their relevance comes from resolution, financial stability, interconnected banking functions and the legal treatment of a failing Spanish bank.

Important Case Laws

1. Banco Santander SA v J.A.C. and M.C.P.R. — Case C-410/20

The Court of Justice delivered its judgment on 5 May 2022 following litigation connected with the resolution of Banco Popular and its acquisition by Banco Santander.

The proceedings concerned the legal consequences of the Banco Popular resolution under the EU bank-resolution framework.

Principle: Resolution law can alter ordinary shareholder and creditor remedies because a failing institution must be dealt with within a framework designed to protect resolution objectives and financial stability.

For network-risk analysis, the case demonstrates how the legal system manages the consequences of failure at an institution integrated into the wider banking system.

2. Fundación Tatiana Pérez de Guzmán el Bueno and SFL v SRB — Case T-481/17

This General Court judgment of 1 June 2022 directly challenged the Single Resolution Board's resolution scheme for Banco Popular.

The litigation addressed the resolution procedure, admissibility, the right to be heard, property rights and the obligation to state reasons under Regulation 806/2014. The action was dismissed as unfounded.

Principle: EU resolution authorities may use the Single Resolution Mechanism when its statutory conditions are satisfied, subject to judicial review and fundamental-rights safeguards.

The decision demonstrates the relationship between institutional failure, regulatory intervention and wider financial-stability objectives.

3. Del Valle Ruiz and Others v Commission and SRB — Case T-510/17

Another major challenge arose from Banco Popular's resolution. The General Court delivered judgment on 1 June 2022.

The applicants challenged matters including the resolution procedure, right to be heard, property rights, delegation of powers and the reasoning supporting the resolution measures.

Principle: Resolution decisions involving systemically relevant banking functions are governed by a specialized legal framework rather than ordinary insolvency principles alone.

For network topology risk, the case demonstrates why authorities need mechanisms capable of dealing rapidly with distress before it disrupts connected financial relationships.

4. Aeris Invest v Commission and SRB — Case T-628/17

Aeris Invest challenged the Banco Popular resolution scheme before the General Court.

The judgment addressed Articles 14, 18 and 20 of Regulation 806/2014 and considered issues including resolution conditions, valuation, property rights, procedural safeguards and the objectives of resolution.

Principle: The resolution of a failing bank must operate according to statutory conditions and safeguards while taking account of the public-interest objectives underlying the EU resolution framework.

5. Aeris Invest v Commission and SRB — Case C-535/22 P

The Banco Popular litigation subsequently reached the Court of Justice on appeal. The Court gave judgment on 4 October 2024.

The case considered the conditions governing adoption of a resolution scheme, the SRB's duties, confidentiality, resolution objectives, sale-of-business requirements and shareholders' property rights.

Principle: Resolution authorities' handling of a failing institution remains subject to legal requirements concerning due care, reasoning, confidentiality, valuation and fundamental rights.

This is relevant to network topology because resolution decisions must simultaneously address an individual institution and the consequences that its disorderly failure could create for the financial system.

6. Banco Popular Resolution Litigation and Article 18 of Regulation 806/2014

The combined Banco Popular judgments—including T-481/17, T-510/17 and T-628/17—provide an important body of jurisprudence concerning Article 18 of the Single Resolution Mechanism Regulation.

Article 18 governs the conditions under which resolution action can be taken, including the assessment that an institution is failing or likely to fail and other statutory requirements.

Principle: Systemic-risk management cannot depend solely on preventive supervision. Banking law also requires a legally structured mechanism for dealing with an institution once preventive measures are insufficient and the statutory resolution conditions are satisfied.

Network Risk Beyond Banks

Modern topology analysis also extends beyond direct bank-to-bank lending.

Banco de España's 2025 map of the Spanish financial system includes investment funds, money-market funds, pension funds, insurers and other financial institutions. It also highlights the importance of international connections and foreign investors in Spanish securities markets.

Consequently, regulators must consider several transmission routes:

Bank → bank: interbank loans and other exposures.

Bank → company: deterioration in corporate credit can weaken lenders.

Bank → sovereign: banks may hold substantial government securities.

Bank → investment fund: common securities exposures or financing relationships can transmit market stress.

Foreign institution → Spanish institution: cross-border funding and investment links can transmit external shocks.

Network analysis is valuable precisely because these channels can interact.

Current Regulatory Importance

Network topology remains relevant to Spanish financial-stability supervision in 2026. Banco de España's Spring 2026 Financial Stability Report, published on 14 May 2026, continues to examine the financial position of Spanish banks and non-bank institutions, market risks, financial-stability risks and macroprudential policy.

Network analysis is also becoming increasingly technological. Banco de España research has explored machine learning and network metrics as supervisory tools for detecting both institution-specific anomalies and broader systemic risks.

Thus, modern supervision increasingly combines legal requirements with granular financial data, stress testing and quantitative network analysis.

Conclusion

Financial network topology risk in Spain concerns the possibility that the pattern of connections between financial institutions can create channels through which losses, liquidity problems or market stress spread throughout the system.

Spanish banking law addresses this risk indirectly but comprehensively through prudential supervision, capital and liquidity requirements, systemic-institution buffers, concentration controls, macroprudential measures, stress testing and the EU bank-resolution framework. Banco de España's network research confirms that understanding interconnectedness is important for identifying potential channels of financial contagion.

The **Banco Popular litigation—C-410/20, T-481/17, T-510/17, T-628/17 and C-535/22 P—**provides the most relevant Spanish-linked jurisprudence for this topic. These decisions do not establish a standalone legal doctrine of "network topology risk"; rather, they show how banking and resolution law responds when distress at a significant financial institution creates broader financial-stability concerns.